I don't know if this is appropriate or even possible in your situation but it is worth a try and takes a few seconds. We have used wifi calling everywhere we travel with no charges at all..no sims...no special calling plan needed...nada....France, Spain, Caribbean but we do have Verizon not T-Mobile but I also did see this on the T-Mobile website:

"Every Wi-Fi connection works like a T-Mobile tower.
You can use your phone to make calls and texts anywhere there’s Wi-Fi. It’s easy. Just connect your phone to a Wi-Fi network and it’s all set. No additional apps, logins or costs required"

Right now...just put your phone in airplane mode (wifi/cell signal will shut off )...turn wifi back on...wait 10-15 seconds....make a call....it should work and ,if it does, it will work ANYWHERE there is a wifi signal with no worries about whether there is a working cell tower where you are. Incoming calls will work like you are at home.Only downside is that you will need wifi.

We go in airplane mode as soon as we get on the plane and stay that way until we return and make as many calls/texts as we want for zero cost.