Bad Service from Cell C and store

I renewed my contract in July 2015. I received the phone at the end of July. After a few days I had problems with the phone. I phoned cell c to explain the problem to them and they booked it for collection to repair. They never collected the phone and after 3 weeks I had to take the it to the cell c shop at the midlands mall in Pietermaritzburg. I couldn't book the phone in that day because cell c never collected and the booking was still on the system. The next day I went back. The phone was sent in for repairs. I received the it back last week and used it for 4 days and are experiencing the same problem again. Yesterday I took the phone back to the store as it is no use to ask cell c to collect because they will book the phone but forget to collect it. I asked the store to include me in the communication between them and cell c and until now have not received anything. By law I have the right to a new device as the \new device"I received in July was in for repairs and still has the same problem. What should I do? I pay for something I can't use and the staff at the midlands mall shop are not helpfull at all not to mention cell c."""