Money taken out of my bank account without permission!

Bought out and closed my contract end of July 2017. 2 August I was debitted for my contract as they didnt close my contract off correctly. After a month of emailing EVERYONE (including the CEO), I was refunded

On 2 October money was taken out of my account without my permission!

No one at MTN will explain: a) Why – if the refund was processed in August – did the account reflect an outstanding amount which was then debited on the 2nd October 2017 ? b) Who gave authority to remove money that does not belong to MTN from my daughters account ? c) What assurance do we have that MTN will not debit this account again ? d) What actions are in place to compensate me for transaction fees ?