Incorrectly debited

After taking up a contract with you guys at the Telkom store in Westwood mall Westville I found my contract to be an absolute pleasure.They had no stock of the device I was interested in(M2 aqua)so the consultant then offered me the Xperia C3(Excellent device)@R299pm with minutes and data which suited my lifestyle perfectly. My number was ported over from Cellc to Telkom mobile in no time... My monthly installments have been successful each month up until I received an sms(03 June 2015)stating that my account is overdue , which is due to non-payment or payment being declined etc.This being shocking to me as I know for sure that I always have enough funds in my account for all my debit orders to be processed. This I ignored and assumed it might have been a system error messages because I still have available fund. (Me being a person who is very aware of how Important it is to keep an excellent credit history am not enjoying this at all) This has only become alarming to me after Telkom has now suspended my account, I now cannot make phone calls or access the internet!