unfair billing

I miss Tinyiko Tinah Nxumalo ID NO: ********** 796081 advise that I entered into a cell phone contract telephonically with Cell C but with Mr Price store. According to the contract it was supposed to be 24 month and was has to pay R129 and get the airtime of R100 and 300MB. I entered into the contract March 2017. The phone was delivered by courier. The first month they debited R200 and when I called them they said its because of admin charges. The second month they called to tell ME that the bill isR600 which was a surprise. I then told them that I wont be able to afford the money and that when they called they never told me about the billing. The agreement was for R129 monthly. I was told that this is open contract and I requested that they change to top up they told me that its not possible. . The deduction increased on monthly basis. I now received the sms stating that the account has been handed over to Daly and they are demanding R3009.50. The reference is ********** and their contact is ********** 608. I need assistance in challenging the this since this is not according to the agreement she telephonically entered into.