Still no Joy!

I have now handed in my cellphone for a third time on 8th April and still no reply from Cell C. The phone is obviously faulty yet they try to fix it and refuse to replace it! I am still paying them every month yet they have my phone. I can't use my sim as I don't have another phone that takes a micro sim and they don't give out loan phones. Their problem is with Sony but I'm suffering :(