Number registered to Apple ID not associated with phone

I see, in that case try signing gout of iMessage and FaceTime and signing back in.

1. Go to Settings > Messages and turn off iMessage.
2. Go to Settings > FaceTime and turn off FaceTime.
3. Restart your device:

• iPhone
• iPad
• iPod touch

4. Turn iMessage and FaceTime back on.

Have you tried going to Settings/Messages and Settings/FaceTime, then removing/unchecking the number? Then sign out of Messages/FaceTime. Restart the phone and sign back in. Enable the number and test.

Just to say, this really helped me when I was in your situation.

1. turn off facetime
2. remove number from imessage
3. turn off phone
4. remove and the reinsert sim
5. turn on iMessage and face time
6. SOLVED

Thank you!!!!

Is the number correct on your Apple ID? Have you tried removing the number, signing out, and then signing back in to add the number again? Allow 24 hours for the change to sync.

Apple ID - Manage    

I fixed this issue by going in to Settings> Phone and changing the ‘My Number’ setting to be the number you brought over from your old network once it has switched. You can then enable this number in iMessage and facetime

Press on "Remove From iMessage and FaceTime".

Is the number correct on your Apple ID? Have you tried removing the number, signing out, and then signing back in to add the number again? Allow 24 hours for the change to sync.

Have you tried signing out of Settings/Your Name, restarting the phone, and then signing back in?

See if anything here helps.

FaceTime and iMessage - Link your phone number and Apple ID for use with.  

Messages or FaceTime - Add or remove your phone number    

Is it your current phone number?

The error message means that this is an old phone number that's different from the phone number on the SIM card that's currently inside your iPhone.

I have the exact same problem, moved to new service provider but transferred old number. Have a warning on iMessage and FaceTime that number is associated with AppleID but not registered on phone. I have tried switching off, powering off and removing sim but warning still persists, my number has 19 days then will expire, anyone know how I can fix this? Thanks

Yes, tried this, still the same problem, number expires in 18 days - any other ideas welcome?