Deregister iMessage number
How do I deregister a number if I no longer have it
iPhone 11, iOS 13
Remove it from your Apple ID. You need to change the number on your Apple ID. After the change, allow up to 24 hours for the change to sync. Before trying to make the change, sign out of Messages/FaceTime on all devices/computers.
See the on-line section.
iMessage on your iPhone or online - Deregister.
