Un-authorised debit order in my account

I called Telkom 2 years ago looking to buy a phone but they kept saying it is out of stock then 3 weeks later I cancelled the contract. now this year in April I get a statement that says I will be debited R2500.00. I immediately called Telkom to enquire about that, they confirmed that there is ***** happening with my personal details and they asked me to send an avadavat and copy of my ID which I did then they sent me a case number. But my cheqque account is still being debited every month and when I call them they say they are still investigating. I'm very irritated by all this. I've lost respect for this company !!!!