Billed more than my signed agreement

I took a MTN my choice 100 contract with Nashua Mobile @R499.00 which includes 100minutes, 100 sms's and 300mg data. In addition to that I added a reoccurring 1 gig to my contract which comes to a total of R648.00 which I have been billed for 6 months from Nashua Mobile. Then in December Nashua Mobile closed down and notified me that MTN will then Debit directly from my account. Since then I've been debited almost double the amount and all they can tell me is that I've charged for the calls and data which I supposed to have gotten on a monthly basis.<br> The call centre has been absolutely no help, no replies to emails. I've been told they would get back to me within 5 business days. That hasn't happened either.<br> I've been with Nashua Mobile for 5 years and not once have I ever experienced such bad customer service and never ever have I been debited a cent more than the contract signed amount.<br>