Wrong again!

After my previous complaint, I took in my Sony Xperia Z3 Compact for repairs a second time on 11 Nov '15th. I got it back on the 26th and it was confirmed that the GPS wss now working. Well, the first time I used it, I found out that it wasn't. Now, it isn't just the time, money and effort spent driving up and down to the service centre. I also have to spend time, effort and about 3gB of data setting up the phone every time it is returned. I don't care if it is a specific technician or Sony SA themselves who messes it up every time. My contract and dealings are with MTN. THEY are *****ing up and I want to know how this is going to be resolved.