***** within MTN

My fiance has been with MTN for 20 years, and two months ago an amount of over R5000 was added to his bill, upon a thousand calls to 135 he was just cut off every time. We were informed by an MTN Employee that this happened to thousands of clients and that there is ***** within MTN. This month another R1000 plus was added for the same, and you just don't get any support from MTN headoffice. They just either put the phone down on you or put you through to a person who does. What should we do?