Custom Formdata matching with user table

Your conditional check is the wrong way around, it should be > not <.

But more importantly, why are you doing a raw SQL query at all, just use the standard functions, e.g. get_user_by:

$user = get_user_by( 'email', $email );
if ( !$user ) {
    // there is no user with that email
}

---

Also, submit is an incredibly generic name for a form input to check, use something more specific, like av_email_cform_submit.

You can also replace your action="' . esc_url( $_SERVER['REQUEST_URI'] ) . '" with action="". You also have a double <p><p> in your form.