INCORRECT DEBIT ON MTN ACCOUNT

After having fought with MTN for 9 months regarding a ********** contract upgrade, they reversed my account to it's normal standing. The right debit order went through for 3 months and then they debited my account with an amount of R2305.24. Again I phoned MTN, advising that these devices are never used and that this billing can't be right (see the history on the account). They said that the best they could do was escalate the problem, which would take anything up to 72 hours to investigate. In my opinion, I do believe that is MTN language for 'you are now bothering me, so please go away whilst we do nothing about it'. I will be cancelling these two MTN contracts that I have, but am worried about doing it prior to something been resolved, as MTN will just state that the account is closed. Is it right that a company like MTN can just do what they like and not have to explain themselves to their customers?