Debit deductions on terminated contract

I had a data contract with MTN. They raised the cost from R299.00 per month to R516 per month without informing me. Upon querying they said it was because of a subscription so I asked them to cancel that subscription and they assured me that the following month that will not be repeated. The following month the problem was still there. After hours and hours of phoning, they gave a different reason and to cut a long story short, I told them I was cancelling the contract. I confirmed by email and reversed the debit order for September.. I have not used their services since my data ran out. Surprisingly this month (October)they debit my account R3 312.42. This is despite the fact that I have not used their services and have informed them I am not interested in their services anymore and I am now using a different service provider. I even had an email from Jacqui Mzobe from their retensions confirming and was asking if I want to retain the number or not. The reference on her email is ***4. What does it take to have MTN cancel this contract and stop debiting my account? Writing them to cancel the contract and stopping using their service is apparently not good enough