OVERBILLING ON ACCOUNT

This is an ongoing struggle since Last year. Mtn has taken over the nashua mobile mtn users, but have failed to do this take over correctly. I am on a set contract inclusive of my BIS and charged correctly by Nashua up until the take over in Nov 2014. MTN over charged me in Nov and corrected/credited my account on Dec Statement.(Please refer to Ticket ref FZG-1***/cr note *** - we were assisted by Marie louise). They Then overcharged in January, feb, march,and ive been logging inquiries since Jan(#***6/Lebogang Kekana) who informed me that my BIS is separate charge as per my contract- which is absolute nonsense since i was refunded for the same error in Dec 2014 and ideally i know what contract i signed into.I have been Instore (Eastrand mall) since i received no response or joy from Customer Care and was helped & advised it was corrected and credit will be affected on my April billing. I have received my April today yet again over debited. This service is pathetic and nobody seems to know what they are doing. Currently this is a bridge of contract as it is not in keeping with what i have signed to be debited of my account and i need someone who can sort this out!