Google forces to use 2FA with SMS authentication, then AT&T disables phone number. Great.
You may be disadvantaged but that number can be transferred to a new phone.
Or, possibly, your existing phone at a new carrier.
https://www.fcc.gov/consumers/guides/porting-keeping-your-ph...
File a complaint with your state AG's consumer protection office.
Most have a specific form (usually online) for telecoms issues.
AT&T is a incredibly consumer-hostile company that does not play by the rules, can and will hold your phone numbers hostage, and as shown here will arbitrarily disable devices when it is convenient for them.