Update on Iphone 5s to iOS 7.1.1 on O2 means i can only get signal in 3G areas

I updated my iPhone 5s software to iOS 7.1.1 yesterday at my friends. When I went home it says "searching" or "no service." I live in a black spot area, but o2 has always been fine before, and still works on my mums pay as you go phone. Previously I had EDGE internet at my house, which creates the problem, I can't get any network (even for just calls and texts) unless I'm in a 3G area. Is there anything I can do other than send it off or go into the store? Is it possible to de-grade my software back to whatever it was before?
ANY help would be much appreciated! I've tried turning it off and on again, I've tried refreshing the search by going on and then off airplane mode, and I tried to be a ninja, running from a place with 3G back to my house and nothing has worked.

Its A Bug In That Version.

Knowing Apple, they never test their products properly, always some bugs in it.

Ask in an Apple store if they can help.

You could try a 'factory reset'.