Complain of Bad service

I have a contract with cell c and every first day of the month I get credited with data (2G) so from this month I never received when I called the branch which assisted me with the contract I spoke to a lady by the name called Nomonde at mall off the north Polokwane . she said I must pay a R150 because the sim card crashed. how do I pay something that's always in the phone and the contract is not even 5 month? please can someone make me understand. or should I just cancel the contract ? my understanding the sim card might be faulty. so must I pay for it? L.P. Magagane ***