$address = (isset($_POST['address']) && ($_POST['address'])) ? $this->qls->Security->make_safe($_POST['address']) : false;
    $city = (isset($_POST['city']) && ($_POST['city'])) ? $this->qls->Security->make_safe($_POST['city']) : false;
    $post_code = (isset($_POST['post_code'])) ? $this->qls->Security->make_safe($_POST['post_code']) : false;
    $telephone = (isset($_POST['telephone']) && preg_match('/^[0-9]{4}[0-9]{7}$/', $_POST['telephone'])) ? $this->qls->Security->make_safe($_POST['telephone']) : false;
    $fax = (isset($_POST['fax']) && preg_match('/^[0-9]{4}[0-9]{7}$/', $_POST['fax']))  ? $this->qls->Security->make_safe($_POST['fax']) : false;

.......
$this->insert_registration_data($username, $password, $email, $address, $city, $post_code, $telephone, $fax, $save);

.....
function insert_registration_data($username, $password, $email) <--- does this has to match top one.