I had to change my phone number / service provider on my phone (iPhone 5s), and while everything else seems to be working OK, I am unable to activate iMessage or Facetime with my new number.
Whenever I go into Settings > Messages or Facetime I turn them on and it says "Waiting for activation..." then after a while (several minutes) it fails "Activation unsuccessful". The phone number shown in Messages and Facetime is my old number (now incorrect) - in this screenshot with area code 664
The phone number in my phone, Apple account and iCloud etc. is my new (correct) number - in this screenshot with area code 661.
I have tried a number of suggestions I've found online: turning off iMessage & Facetime and restarting phone; changing phone number and changing back; signing out of AppleID throughout phone then signing back in - however I still can't activate them.
Please note that facetime and imessage are working fine using my appleID, and I'm able to send/receive SMS (including SMS from Apple).
The issue seems to be that Messages/Facetime is trying to activate on the old number but I can't change that number to the new one.
How can I change that activation phone number and activate iMessage and Facetime for my new number?