No service with new SIM card, Sprint to T-Mobile

I've had my service for about 12 years now. Last summer I talked to the T-Mobile rep in a nearby city and was flat out told not to switch SIM cards because there was no coverage anywhere. This spring I had to replace my stolen phone and the SIM card is T-Mobile. I've called and gone into multiple stores, but stores tell me the towers are all the same now and a SIM card wouldn't help. Tech support says they'll send out a signal booster and a different SIM card, but it's been 3 months and they still say they're waiting on inventory. Sprint never had what you would call good coverage here, about .7mbps average for data, but if I left my house it was passable and I could at least stream Netflix most of the time at home. I stayed with Sprint for the unlimited data, but that's kind of a joke when you can't hardly stream a low quality movie. Still, it worked. At this point, I don't get enough service to make a phone call at home. Text messages come in days late if at all. Data usage is flat out impossible. That's at home. At work my phone is in a dead zone. There's zero function at all within 5 miles of work. The 70 miles between those 2 points is no better, GPS coverage is non-existent as well, navigation is so bad it can't even start the route. Mind you, I'm not in some insanely remote area. My phone stops working 10 min outside the capital of Michigan. I live 30 miles centered between 5 major cities in Michigan, the number 2, 3, and 5 largest population centers among them. At no point am I ever further from that and I'm almost always under 20 miles from a large city. In fact I can stand inside of 2 different T-Mobile stores in 2 different cities 40 miles apart, and it doesn't function consistently in either. I also started a second line in April, 2 days after supposedly Sprint and T-Mobile SIM cards were combined and Sprint only cards were phased out. That phone gets crappy service, but it's about what I expected from Sprint and the crappy coverage they provided. At this point, my phone is a paper weight everywhere I go and anyplace under an hours drive. What am I supposed to do here besides cancel my service?