@ErikaEToth The US started shutting their 3G networks down in February 2022. Mine was fine in June 2022, but when I went in November 2022 i had no service for phone calls. It's location and roaming partner dependent though. By spring 2023 PM started rolling out VoLTE, but only to select devices; your phone unfortunately is not on their approved list, so unless you can find a 2G service to connect to, you won't be able to make phone calls.
When was the last time you were there and were able to make calls?
What add-on did you buy? Just calls? Calls and texts? Calls, texts, and data? Do texts and data work?
What phone do you have? The US no longer has a 3G network, so it's important that you have VoLTE to be able to make phone calls. Knowing what phone you have will help determine whether you have VoLTE or not.
Also are you able to connect manually to T-Mobile?