model->save() Not Working In Yii2

Previously, I was not using $model->save() function for inserting or updating any data. I was simply using createCommand() to execute query and it was working successfully. But, my team members asked me to avoid createCommand() and use $model->save();

Now, I started cleaning my code and problem is $model->save(); not working for me. I don't know where i did mistake.

UsersController.php (Controller)

<?php
namespace app\modules\users\controllers;
use Yii;
use yii\web\NotFoundHttpException;
use yii\filters\VerbFilter;
use yii\swiftmailer\Mailer;
use yii\filters\AccessControl;
use yii\web\Response;
use yii\widgets\ActiveForm;
use app\modules\users\models\Users;
use app\controllers\CommonController;

class UsersController extends CommonController 
{
    .
    .

    public function actionRegister() {
    $model = new Users();

        // For Ajax Email Exist Validation
   if(Yii::$app->request->isAjax && $model->load(Yii::$app->request->post())){
     Yii::$app->response->format = Response::FORMAT_JSON;
     return ActiveForm::validate($model);
   } 

   else if ($model->load(Yii::$app->request->post())) {
      $post = Yii::$app->request->post('Users');
      $CheckExistingUser = $model->findOne(['email' => $post['email']]);

      // Ok. Email Doesn't Exist
      if(!$CheckExistingUser) {

        $auth_key = $model->getConfirmationLink();
        $password = md5($post['password']);
        $registration_ip = Yii::$app->getRequest()->getUserIP();
        $created_at = date('Y-m-d h:i:s');

        $model->auth_key = $auth_key;
        $model->password = $password;
        $model->registration_ip = $registration_ip;
        $model->created_at = $created_at;

        if($model->save()) {
          print_r("asd");
        }

      }

    } 
    }
    .
    .
}

Everything OK in this except $model->save(); Not printing 'asd' as i echoed it.

And, if i write

else if ($model->load(Yii::$app->request->post() && $model->validate()) {

}

It's not entering to this if condition.

And, if i write

if($model->save(false)) {
    print_r("asd");
}

It insert NULL to all columns and print 'asd'

Users.php (model)

<?php

namespace app\modules\users\models;

use Yii;
use yii\base\Model;
use yii\db\ActiveRecord;
use yii\helpers\Security;
use yii\web\IdentityInterface;
use app\modules\users\models\UserType;

class Users extends ActiveRecord implements IdentityInterface 
{

  public $id;
  public $first_name;
  public $last_name;
  public $email;
  public $password;
  public $rememberMe;
  public $confirm_password;
  public $user_type;
  public $company_name;
  public $status;
  public $auth_key;
  public $confirmed_at;
  public $registration_ip;
  public $verify_code;
  public $created_at;
  public $updated_at;
  public $_user = false;

  public static function tableName() {
    return 'users';
  }

  public function rules() {
    return [
      //First Name
      'FirstNameLength' => ['first_name', 'string', 'min' => 3, 'max' => 255],
      'FirstNameTrim' => ['first_name', 'filter', 'filter' => 'trim'],
      'FirstNameRequired' => ['first_name', 'required'],
      //Last Name
      'LastNameLength' => ['last_name', 'string', 'min' => 3, 'max' => 255],
      'LastNameTrim' => ['last_name', 'filter', 'filter' => 'trim'],
      'LastNameRequired' => ['last_name', 'required'],
      //Email ID
      'emailTrim' => ['email', 'filter', 'filter' => 'trim'],
      'emailRequired' => ['email', 'required'],
      'emailPattern' => ['email', 'email'],
      'emailUnique' => ['email', 'unique', 'message' => 'Email already exists!'],
      //Password
      'passwordRequired' => ['password', 'required'],
      'passwordLength' => ['password', 'string', 'min' => 6],
      //Confirm Password
      'ConfirmPasswordRequired' => ['confirm_password', 'required'],
      'ConfirmPasswordLength' => ['confirm_password', 'string', 'min' => 6],
      ['confirm_password', 'compare', 'compareAttribute' => 'password'],
      //Admin Type
      ['user_type', 'required'],
      //company_name
      ['company_name', 'required', 'when' => function($model) {
          return ($model->user_type == 2 ? true : false);
        }, 'whenClient' => "function (attribute, value) {
          return $('input[type=\"radio\"][name=\"Users[user_type]\"]:checked').val() == 2;
      }"], #'enableClientValidation' => false
      //Captcha
      ['verify_code', 'captcha'],

      [['auth_key','registration_ip','created_at'],'safe'] 
    ];
  }

  public function attributeLabels() {
    return [
      'id' => 'ID',
      'first_name' => 'First Name',
      'last_name' => 'Last Name',
      'email' => 'Email',
      'password' => 'Password',
      'user_type' => 'User Type',
      'company_name' => 'Company Name',
      'status' => 'Status',
      'auth_key' => 'Auth Key',
      'confirmed_at' => 'Confirmed At',
      'registration_ip' => 'Registration Ip',
      'confirm_id' => 'Confirm ID',
      'created_at' => 'Created At',
      'updated_at' => 'Updated At',
      'verify_code' => 'Verification Code',
    ];
  }

  //custom methods
  public static function findIdentity($id) {
    return static::findOne($id);
  }

  public static function instantiate($row) {
    return new static($row);
  }

  public static function findIdentityByAccessToken($token, $type = null) {
    throw new NotSupportedException('Method "' . __CLASS__ . '::' . __METHOD__ . '" is not implemented.');
  }

  public function getId() {
    return $this->id;
  }

  public function getAuthKey() {
    return $this->auth_key;
  }

  public function validateAuthKey($authKey) {
    return $this->auth_key === $auth_key;
  }

  public function validatePassword($password) {
    return $this->password === $password;
  }

  public function getFirstName() {
    return $this->first_name;
  }

  public function getLastName() {
    return $this->last_name;
  }

  public function getEmail() {
    return $this->email;
  }

  public function getCompanyName() {
    return $this->company_name;
  }

  public function getUserType() {
    return $this->user_type;
  }

  public function getStatus() {
    return $this->status;
  }

  public function getUserTypeValue() {
    $UserType = $this->user_type;
    $UserTypeValue = UserType::find()->select(['type'])->where(['id' => $UserType])->one();
    return $UserTypeValue['type'];
  }

  public function getCreatedAtDate() {
    $CreatedAtDate = $this->created_at;
    $CreatedAtDate = date('d-m-Y h:i:s A', strtotime($CreatedAtDate));
    return $CreatedAtDate;
  }

  public function getLastUpdatedDate() {
    $UpdatedDate = $this->updated_at;
    if ($UpdatedDate != 0) {
      $UpdatedDate = date('d-m-Y h:i:s A', strtotime($UpdatedDate));
      return $UpdatedDate;
    } else {
      return '';
    }
  }

  public function register() {
    if ($this->validate()) {
      return true;
    }
    return false;
  }

  public static function findByEmailAndPassword($email, $password) {
    $password = md5($password);
    $model = Yii::$app->db->createCommand("SELECT * FROM users WHERE email ='{$email}' AND password='{$password}' AND status=1");
    $users = $model->queryOne();
    if (!empty($users)) {
      return new Users($users);
    } else {
      return false;
    }
  }

  public static function getConfirmationLink() {
    $characters = 'abcedefghijklmnopqrstuvwxyzzyxwvutsrqponmlk';
    $confirmLinkID = '';
    for ($i = 0; $i < 10; $i++) {
      $confirmLinkID .= $characters[rand(0, strlen($characters) - 1)];
    }
    return $confirmLinkID = md5($confirmLinkID);
  }

}

Any help is appreciable. Please Help me.