Question about cellphone number after porting it to a new cellphone provider.

This number is registered to your apple id but not associated with your iphone

Good morning. This is concerning iPhone 13 on 17.4.1. DH has changed cell phone provider, his cell phone number was ported to the new provider, he has been using his iphone for about a month with this new provider. Now he has a message that says “this number is registered to your apple id but is not associated with this iphone. You can keep using the number for iMessage and Facetime but it will expire in 4 days!”.

He has checked - this number appears in settings - iMessage and Facetime in Receive Messages to and reply from, and in start new conversations from.

He has turned both iMessage and Facetime off, waited and turned it back on. No Change.

He has turned both off and turned iphone off, turned everything back on. No Change.

Will this resolve itself either before or after the 4 day expiry or is there something else he should do?

Thank you for any help.