MTN POOR CUSTOMER SERVICE

I cancelled my contract on expiry date on the 26th November. For the passed 3 months they keep on debiting my bank account because apparently your contract is in arears. How ever an increase amount was debited to my bank acc and i reversed thè debit order. I have been trying for 3 months now to stop them to debit my account. When i phone @ my cost Customer service. They say my nr or ID do not acsist on their system however my bank acc nr still exist. Please never sign a contract with them because you can not get rid of them