Can’t remove old phone number from iMessage and FaceTime

I tried several way to remove old phone number from my apple acoount ( and imessages and Face time) . I followerd prcedure on " online " but Apple required passcode on old phone number. but I don't hae the old phone number. I can't receive it. How do i do?

[Re-Titled by Moderator]

Original Title: deregiter imessage for old phone number