PHP form not saving information to SQL database

I'm currently working on a project that has a registration form that should theoretically work as far as I know for the registration but I can't seem to identify what I'm doing wrong.

The code below is the front-end section for the registration form

<form style="border: 3px solid #ddd; border-radius: 10px; padding: 10px;" class="uk-form-stacked js-register">

        <div class="uk-margin">
            <label class="uk-form-label" for="form-stacked-text"><b>Username:</b></label>
            <div class="uk-form-controls">
                <input id="user_name" style="border-radius: 10px;" class="uk-input" name="form-stacked-text" type="text" required='required' placeholder="Insert Username">
            </div>
        </div>
        <div class="uk-margin">
            <label class="uk-form-label" for="form-stacked-text"><b>Email:</b></label>
            <div class="uk-form-controls">
                <input id="user_email" class="uk-input" style="border-radius: 10px;" name="form-stacked-text" type="email" required='required' placeholder="Insert Email">
            </div>
        </div>
        <div class="uk-margin">
            <label class="uk-form-label" for="form-stacked-text"><b>Password:</b></label>
            <div class="uk-form-controls">
                <input id="user_pass" class="uk-input" style="border-radius: 10px;" name="user_pass" type="Password" required='required' placeholder="Insert Password">
            </div>
        </div>
        <div class="uk-margin">
            <label class="uk-form-label" for="form-stacked-text"><b>Confirm Password:</b></label>
            <div class="uk-form-controls">
                <input id="user_pass_check" class="uk-input" style="border-radius: 10px;" name="user_pass_check" type="Password" required='required' placeholder="Confirm Password">
            </div>
        </div>
        <div class="uk-margin">
            <div class="uk-form-controls">
                <div class="captcha">

                    <div align="center" class="g-recaptcha" data-sitekey="-" data-callback="recaptcha_callback"></div>
                </div>
                <br>
            </div>
        </div>

        <div class="uk-margin uk-alert-danger js-error" style='display: none;'></div>

        <div class="uk-margin">
            <label><center>Already have an account? <a href='/~za1180x/comp1687/login.php'>login now!</a></center></label>
            <br>
            <center><button id="registerbtn" name="registerbtn" class="uk-button uk-button-default"  type="submit"><b>REGISTER</b></button></center>
        </div>

    </form>

The backend code responsible for submitting the information to the database is as follow

if($_SERVER['REQUEST_METHOD'] != 'POST')
{
    $return = [];
    $email = Filter::String( $_POST['user_email']);
    $password = Filter::String( $_POST['user_pass']);
    $username = Filter::String( $_POST['user_name']);

    $user_found = User::Find($email, $username);

    mysqli_report ( MYSQLI_REPORT_ALL);

    if($user_found) {
        // User exists
        // We can also check to see if they are able to log in.
        $return['error'] = "You already have an account";
        $return['is_logged_in'] = false;
    } else  {

        // User does not exist, add them now.
        $password = password_hash($_POST['password'], PASSWORD_DEFAULT);
        // make sure the user CAN be added AND is added.
        $addUser = $con->prepare("INSERT INTO users(user_name, user_email, user_pass) VALUES(:user_name, LOWER(:user_email), :user_pass)");
        $addUser->bindParam(':username', $username, PDO::PARAM_STR);
        $addUser->bindParam(':email', $email, PDO::PARAM_STR);
        $addUser->bindParam(':password', $password, PDO::PARAM_STR);
        $addUser->execute();

        $user_id = $con->lastInsertId();

        $_SESSION['user_id'] = (int) $user_id;

        $return['is_logged_in'] = true;

        $return['redirect'] = 'C:\wamp64\www\index.php?message=welcome';


    }
    // return the proper information back to Javascript to redirect us.

    echo json_encode($return, JSON_PRETTY_PRINT);
} else {
    //Kill the script. Redirect the user.
    exit('Invalid URL');
}

The code below is the class that I've created that makes the connection for the database.

class DB {

    protected static $con;

    private function __construct(){
        try {

            self::$con = new PDO( 'mysql:charset=latin1;host=localhost;port=3306;dbname=webenterprise', 'root', ''); //change connection string
            self::$con->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );
            self::$con->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_SILENT);
            self::$con->setAttribute( PDO::ATTR_PERSISTENT, false );
            self::$con->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);

        } catch (PDOException $e) {
            echo "Could not connect to database."; exit;
        }
    }


    public static function getConnection() {
        //If this instance has not been started, start it.
        if (!self::$con) {
            new DB();
        }
        //Return the writeable db connection
        return self::$con;
    }

   }