Awaiting refund , contract cancelled , debit order still operating

At the end of May 2017 i telephoned the Call Centre to cancell my contract of R69 pm. I was advised that cancellations could not be accepted telephonically and had to be in writing and i sent an email. On the 10 August i received an SMS confirming cancellation . but the debit order continued to operate off my account. i teleponed Call centre about 7 November and they said they would ask the Billing Department to arrange a refund as cancellation had been confirmed, The debit order was generated at the end of November which i stopped payment with the Bank and i again telephoned them. They advised that the billing Department declined a refunds because i owed them in excess of R1000 for out of bundle rates and that the Bank had returned my debit order due to lack of funds from January 2017 to May 2017 when they tried to recover the arrears. They needed copy of my bank statements to prove otherwise. I sent copies of my bank statements from January to May confirming that in excess of R2100 had been collected for the out of bundle rates. Despite several follow up mails they have not responed to how the arrears of R1100 arose despite the R2100 having been collected. They simply do not respond to emails other than to advise that they will continue to collect the R69 pm until the arrears have been repaid. I have a clean record with the Bank am a Private Clients customer and there is more than enough money to collect their debit order which included the out of bundle rates from January to May which averaged R460 pm. I need an explanation and the refunds. I tried to speak to a Supervisor and the Billing Department was told by the Call Centre Agent that they do no take calls and if i have a problem i must send a email to their Support Centre which i did.