Deregister
What to do if you lost your sim card, and it’s still registered at iMessage and Facetime?
iPhone 8 Plus, iOS 13
What to do if you lost your sim card, and it’s still registered at iMessage and Facetime?
iPhone 8 Plus, iOS 13
if you don't plan on just having your carrier provide you with a new sim with the same number then you can
Add or remove your phone number in Messages or FaceTime – Apple Support
Deregister