Unable to connect to cellular data. Help

Two weeks ago I lost the ability to connect to cellular data. iPhone 7, T-Mobile account in good standing. Powering down the phone and back on fixed the issue briefly but then it failed again and hasn’t been right since. Took it to the T-Mobile store, replaced the SIM card to no avail, so they believed since the phone was old it was time for a new phone. Once again, the account is in good standing. So, I purchased an SE 3rd generation phone, refurbished, from Mac of all Trades, transferred data over to the new phone from the old and have the EXACT same problem. Can only use the phone for SOS calls and can iMessage other Apple users. Then took it to an Apple Store, technician suggested a hard reset of the entire device. Which I did. Still doesn’t work. As a matter of fact one could argue it’s worse now as I can’t get the iMessage function to work. Surely I didn’t have a iPhone 7 for some 7 odd years finally go bad, then bought a new (refurbished) phone that has the exact same issue? What are those odds?

if I place the SIM card into another phone, it works, put it into my wife’s even older iPhone 6 and it works fine, as a communication device should, so one would surmise it’s a software or hardware issue.

Any help would be appreciated. Hopefully there is an Obi-Wan out there.