Where you live might play a role in figuring out which cell site (="tower") might be giving you fits, if that's the trouble. Have you determined whether or not you are on an area of 'fringe' 4G reception for T-Mobile? Does the phone work better if you try it *outdoors* vs indoors? How about places not far from where you reside?

If possible would you be willing to post a major cross street/zip code near where you live so we could look online at the current coverage maps w/ T-Mo? I would have to see that info in order to make a recommendation, although sales generally isn't the best channel for such support IME. They sell things, they do not provide first line technical knowledge.