What happens if you turn off LTE? Has the phone sustained any damage recently? Are you in the same area you normally are in? Is voice working for you? How about WiFi?
What happens if you turn off LTE? Has the phone sustained any damage recently? Are you in the same area you normally are in? Is voice working for you? How about WiFi?
Call ATT and have them verify that your phone and account both have the same IMEI and CCID numbers set. Have them reset both even if they are correct and see if that helps.