Debit order cancellation

I do not have regular income and it happens that when Telkom debit orders go off my current account there isn't always funds. This results in Telkom adding penalties to my account even though I make payment via THEIR website, on or before the due date. To prevent unnecessary charges being added to my account by Telkom, I decided to cancel the debit order and make all future payments manually. Telkom refused to honour my request and apparently it is not possible to cancel the debit order. But if I pay my account 14 days before the due date they promise not to debit my account. I refuse to accept that. My bank account belongs to me and Telkom does not have the right to decide how my personal bank account is managed. The gentleman that assisted me was Mduduzi, unfortunately I did not note his surname. He had the audacity to tell me that Telkom is not my bank and when I asked him what he meant by that he became rude and overbearing on the telephone. Then his supervisor told me the same thing but she was a lot more civil. Herewith, I withdraw the authority that Telkom has to debit my account for any reason whatsoever. I want Telkom to cancel the debit orders on my bank account, for all three accounts that I have with Telkom. I do not want any more unnecessary additional charges added to my account by Telkom. To add to my frustration, not Mduduzi or his supervisor were able to tell me who to speak to in order to cancel the debit order. My hope is that somebody who works there will see this and point me in the right direction so that I can send my formal debit order cancellation to the correct person or department.