Calling index() on form validation failure

Hi, sorry for the delay:
CI 3.1.

I have already added the error to /system/language/english/form_validation_lang.php

Custom Helper (which worked for non-required as a callback_ when in the controller):

PHP Code:

if ( ! function_exists('customAlpha')) {
    function customAlpha($str)
    {
        if (!preg_match('/^[a-z .,\-\']+$/i', $str)) {
            return FALSE;
        } else {
            return TRUE;
        }
    }
}