We switched providers and it has been 30 days and we received a msg that says: this number is registered to your Apple is but is not associated to this phone. We can continue to use it until it expires. Something seems to be set up wrong on this and need help so we can continue to use iMessage and FaceTime.
iPhone XR, iOS 14
Hi Smithport,
Wondering if your phone number was changed when you changed providers.
Your Apple ID is the account that you use to access all Apple services,
including iCloud, iTunes, Music, App Store, iMessage, FaceTime, and more.:
Sign in with your Apple ID
https://support.apple.com/en-us/HT204974
If you forgot the answers to your Apple ID security questions
https://support.apple.com/en-us/HT201485
Having trouble signing in?
https://iforgot.apple.com/password/verify/appleid
NB: This article:
How to get a verification code and sign in with two-factor authentication
https://support.apple.com/en-gb/HT204169
Says:
Update your trusted phone number on your Apple ID account page
If you want to add a phone number, click Add a Trusted Phone Number and enter the phone number. Choose to verify the number with a text message or automated phone call, and click Continue. To remove a trusted phone number, click 
next to the phone number you want to remove.
If you need more help:
Apple ID Support Page:
https://support.apple.com/en-au/apple-id
Or
Contact Apple for help with Apple ID account security:
https://support.apple.com/en-gb/HT204169
And:
Add or remove your phone number in Messages or FaceTime
https://support.apple.com/en-us/HT201349
Hope one or more of these articles help you achieve your goal ok :)
Registering a phone number to an Apple id
