Unknown outstanding balance

I have a problem with MTN, october first i had a deduction of R750 on account of which i disputed it because for what i know i had a credit toward the end of my contract in September. In july a debit order was made on account of which they refused to refund me back. When i check my app today im seeing R906, as an outstanding i dnt know for what. What is confusing no one knows how did it even happen that i am owing. Customer care does not help at all, they kept of giving me reference numbers when i do a follow up, there is not update.