CELL C - cant fix my problem

I renewed my contract beginning 2014 and the phone I chose was a Samsung galaxy s4. First couple of days it worked just fine, but then the problems Started. Although the signal bar will shows full signal no calls will come through, only when I restart the phone will all the miss calls come through. I have logged several calls at cell c call center, but their standard answer is, take it to cell C repair center in Tygervally, which I have done 3 times before. The Cell C repair center tygervally told me to take the Samsung galaxy S4 to Samsung store also in Tygervally. I have done that only to be told my phone is perfect no problem and I must go back to Cell c repair center in tygervally. Cell C tygervally replaced my sim card and say that the problem will now be fixed. It still is not fixed and I have the same problem. Well it was back to the call center only to be told again to go to the cell C repair center. I have phoned the repair center once again only to be told I need to book the phone in again for another 21 days.My Question is. How many times must this happen, until the warrenty run out I suppose. this will be my last cell c contract.