You can call or message T-Mobile on social media and create a coverage Network ticket. That will let the engineers know about your area however until that time comes when you have native coverage you can always try a cellspot router or LTE cellspot with high-speed internet. Both are available for free or a small deposit of $25 and can really fill in the gap for you.
I have a similar situation with a vacation cabin. Dead spot for about 100 yards around. Fortunately, WiFi Calling takes care of the problem.
North Carolina is a tough market for T-Mobile as there wasn't a lot of available spectrum in NC when TMO launched nor thru any of their acquisitions because a lot of the spectrum in NC was bought by 3rd parties, some for investment purposes and others for smaller regional carriers. Now this has gotten a bit better over recent years and TMO was able to get some 700 in NC from Verizon but not even Verizon had any to give in Raleigh/Chapel Hill area of NC. So all TMO has is the mid high band (band 2 and/or 4) which is much more limited in range (generally 4 towers to 1) and also can get around (penetrate) trees, buildings and etc as easy. I know before Band 12 in my market during the spring/summer at my old house my signal dropped 2 bars because the trees all filled in and at my new place until band 12 had no coverage unless I drove out of the development because its in a geographic bowl and surrounded by trees.
Your market will get 600 but in reality dependent on what tv stations are in your market could be a year to 3 years out. As mentioned Wi-Fi calling is a great alternative get around that if you have Wi-Fi available. The other option is and LTE cellspot which essentially puts an LTE antenna in your home with about 3,000 sqft of LTE coverage and all it needs is a broadband connection. On advantage of the latter is that if you start a call on the cellspot you in theory can walk out of your home and as long as it doesn't lose coverage before seeing a local tower the call will handoff to the "real" cell network. TMO will send you an LTE cell spot for free with a $25 deposit so they can encourage you to give it back if you leave TMO :-)