Are you using a physical SIM or eSIM? Years ago when I had T-Mobile, was unable to receive most text messages. I finally went into a store and they gave me a new SIM card. The issue cleared up right away.

I've had issues somewhat recently sending SMS' to one contact in particular. Still unsure it that was an iOS or AT&T problem. Reset network settings and haven't seen the problem reappear in the past few days.