Cell C Sim Card not working

I have a contract phone with Cell C. I have this phone 6 months now and have already did 3 sim swops as the sim card just stops working. The sim card is never taken out of the phone. Whenever this happens Cell C just says that the sim card might be faulty and I would have to do a sim swop. How can every sim card be faulty? How the hell can I pay R150 to do a sim swop when its not even my fault that the sim card is faulty. This is really unacceptable. This is absurd. Currently the sim card is again not working for the fourth time now. All the lady says is the sim card shows active on her side but the sim card does not even pick up in the phone. This is really bad service.