Unauthorized debits from Telkom

I had a data contract with Telkom which expired in May/June, I cancelled the contract before expiry online with the help of an agent and got a reference number but they still debit my account to date. I have called to query this and keep getting told "Sorry we will fix this" but it never gets fixed. I have disputed and stopped the debits but this month they came with a different amount. My account gets debited but the sim doesn't get data anymore. What exactly am I paying for here!!!!