BILLING ERROR NOT RECTIFIED

Approximately 6 weeks ago my husband noticed that his MTN account was double the amount it should be. He went into an MTN store to ask for assistance. The consultant told him that as he had taken out the upgrade telephonically, they could not help him in the store and he should call the promotion company who sold him the upgrade. He called the promotion company. He was told 3 different stories by 3 different consultants. One amount of R104/month was a billing error. The other amount of R460/month was a Black Friday promotion. Not one of those 3 people rectified the problem. My husband then called MTN directly and once again has spoken to 3 or 4 different people. They all promise that they will log the complaint and that it will be rectified. The last person he spoke to on Friday 31 July said the complaint had been logged with the billing department and an sms would be sent on Wednesday 5 August to say that the billing error had been reversed and he would be credited with the erroneous charges. It is Wednesday 5 August today. So far no sms. HOW CAN MTN ALLOW THESE DEBITS TO BE CHARGED WITHOUT AUTHORIZATION FROM THE CLIENT? AND WHY DOES IT TAKE SO LONG TO RESOLVE A "BILLING ERROR"?