Notice Messages Do Not Appear On The Page

I’m working with PHP OOP to develop my custom management system. Basically, I created a page which Admins can add another custom admin. Here is the code:

if (isset($_POST['submit'])){
    $username = $_POST['uname'];
    $email = $_POST['email'];
    $password = $_POST['pass'];
    $groups = $_POST['groups'];
    if (filter_var($email, FILTER_VALIDATE_EMAIL) === false) {
        $notice['email_validation'] = "The email that you have entered is not a valid one";
    }else{
        $registration = new Admin();
        $notice[] = $registration->CheckUname($username,$email,$password,$groups,$level);   
    }   
    $notice = $registration->getNotice();
}

As you can see at the end, I had specified a variable called $notice which is calling a method getNotice() and it goes like this:

public function getNotice()
{
    return $this->notice; 
}

And the notice variable here is set protected. So the form itself works fine but it just don’t show me any error/success message.

Actually I had added also these codes at the main page that contains the form in order to output the error/success messages:

if(isset($notice['email_validation'])) {
    echo "
    <div class='alert alert-danger'>
        <strong>Hey!</strong> ".$notice['email_validation'].".
    </div>
    ";
}
if(isset($notice['username_exists'])) {
    echo "
    <div class='alert alert-danger'>
        <strong>Hey!</strong> ".$notice['username_exists'].".
    </div>
    ";
}
if(isset($notice['email_exists'])) {
    echo "
    <div class='alert alert-danger'>
        <strong>Hey!</strong> ".$notice['email_exists'].".
    </div>
    ";
}
if(isset($notice['success_message'])) {
    echo "
    <div class='alert alert-success'>
        <strong>Hey!</strong> ".$notice['success_message'].".
    </div>
    ";
}

So if you know what am I doing wrong, please let me know I would really appreciate that.

Also note that the page does not return any PHP errors while the error reporting is on!

if (filter_var($email, FILTER_VALIDATE_EMAIL) === false) {
    $notice['email_validation'] = "The email that you have entered is not a valid one";
} else {
    $registration = new Admin();
    $notice[] = $registration->CheckUname($username,$email,$password,$groups,$level);   
}   

$notice = $registration->getNotice();