getting billed long after contract is settled

I cancelled my contract, paid the penalty and sent the proof of payment. This was in April. In July, the same debit order started running again. I called mtn, they sent an sms confirming cancellation and I was told that I would be refunded. I have not been refunded and now they've taken(****** basically) more money.<br> <br> I ported because of this(hoping the debit orders would end too) and the fact that the service is just terrible everywhere I go. But still, they debit my account.