Not happy with service and turnaround time

I took up a contract with MTN, a while back and I have never used my MTN sim I have only used the device. Therefore I have been paying a flat rate of R349.00 monthly until most recently in January 2015 I was billed R 993.00 I am billed in areas so i only picked up on the debit this month. I am disputing this amount as I have never used my sim before. For March I have been billed another R660.80 I don't know where this amount comes from I can't even afford it. I don't think it's fair to pay for something I have not used. I called MTN today re number: *** spoke to Busisiwe I was still unhappy and requested to speak to a manager and I was told I will be contacted within 24 hours. The lady has reported this to the ***** department but my argument is I did not make those calls and use up that data. Why should I pay for it then