Get a PAYG SIM and try it .. only way I'm afraid, you cannot believe any coverage maps. According to them my village has very patchy coverage but I get great signal and speeds.
M
I'm currently on a 1 month rolling plan, so I'd be looking at getting another 30 day contract and seeing what happens with the network maybe?
The other way round would be to
Sign upto 12 months with T mobile.
I'm not in the town centre either, in a village called sprotbrough. But signal seems ok on the map. (I know it's best to try it out 1st.