UNAUTHORISED debit order from my bank account

I logged a request to cancel my contract a few month ago. I received an email stating I will have to pay in R6700. So I did not respond to the email, as it was too much to pay in and I could not afford it. This morning, a DEBIT order went off my bank account for R6700, for Telkom. HOW was this allowed?? I did not give consent ANYWHERE for a debit amount to be taken off my account other than the current monthly installments. Just when you think the service and products can't get worse it does! This is not acceptable. They don't have ANY documents where I gave consent to go ahead with the cancellation of the service as well as the SIGNED document where I confirmed they can debit off the cancellation fee from my bank account. I WANT MY MONEY BACK TELKOM