phone was taken in 2 times for over heating

I took my phone in because it overheated. When I got it back they said it was not software update. The same day that in took the phone and setting it up again it started with the same problem again overheating barest draining and freezing. I took it back again. After 3 weeks they tel me nothing was wrong. But it is still over heating freezing and draining my battery. The problem is still not solved It feels like the phone is going to explode if I use it.