Worst service ever.

I reported them here and there's still no response. How can I be in arrears for a prepaid service that I pay every month? They debit my account on the 1st and payments are normally paid by the 15 to the 20th or so. Now they say I owe then R958. 00 and I'm not receiving a satisfactory explanation. I have provided them with my credit card statement which shows all the payments monthly and they told me about a system upgrade. I sent an email on the 6th of April and I'm not getting joy from Confidence Keupilwe.