Well, I just lost data service again after less than 24hr after upgrading my plan from T-Mobile Connect with 3.5GB Data per month, to "TMobile Prepaid unlimited", with unlimited data. All I did was watch a couple of YouTube's using the app, and Browse AT Forums a bit.
Either I'm on a watch list (without due process!), or I've made T-Mobile's internal "shit list" of customers that they screw over until they leave the service, and even upgrading from the $15/mo plan (that I was DENIED my 3.5GB / mo of data) to their UNLIMITED $50/mo plan, wasn't enough to make amends, apparently.
I know this, because I've been through multiple 4G LTE phones, all were technically-compatible with T-Mobile's service. One time, on a whim, I purchase an allotment of 'Domestic Data', for a week, AND I HAD WORKING DATA.
Like this time, I switched to an unlimited data plan, and it was working, until they found out and shut me down.
I'm not even using that much data. I'm not hotspotting, either.