unhappy with service want to cancel contract

i have a a defective simcard and cell c are not helping me resolve my problem since sunday. i have complained on monday and i got feedback later that afternoon of what to do but it didnt work. i complained on tuesday they told me that they have resolved the problem and told me remove simcard and re booth phone which i did but it still didnt work. i phoned back on wednesday at 8 30 to complain again i spoke to nathaniel in porting who gave me a case number and told they will contact me but i didnt hear from them so i called at 12 30 and was told the same by another agent at call center but no contact was made with me. i phoned again on thursday morning at 8 to log another complain coz i still hadnt received feedback from my case i was told they will contact me once problem is resolved. i phoned again at bout 12 05 and was more than half and hour on the phone and was promised by mr thato modaudze that by the end of business on thursday he will definately call me back but nobody has called me. i made it clear to them that i want to cancel my contract as im sitting without a phone from sunday and paying for the service. i was told to cancel i must pay R2700,80. im not willing to pay.