Debiting my account for years post cancellation

Ive cancelled my contract with telkom many years ago and despite calls, standing in ques, shop visits and many many hours spent trying to get them to pay back my premiums that was debited and stop the debit order it still continues.

I cancelled the contract in store and no proof was given that I recall, when I do get through, I get asked for proof of cancellation or they cant do anything.