Phone say server unavailable

When I go to make a call it says my server is unavailable on my phone. I have full bars but can't make calls and if I get a call or it goes thru it drop it within a second. Or they can't hear me answer the phone. When I went to the local T-Mobile store they said it was do to the cell towers. But this is going on 2 weeks. Have tried calling support but it drops the call before the automated gets to where I can say anything. Any ideals as to how I can get thru to them, I don't have access to another phone. I am not downloadin an App to my computer.