BIS Charge Credit

A month ago I called MTN with regards to them billing for BIS on my samsung phone for the past 19 months. The person I spoke to assured me that they would credit my contract account with the 19 months worth BIS that was charged in error on both my contracts and I was told that the query has been escalated to the billing department for approval of the credit, and that if the credit was granted I would only be billed for what was owing less the credit (in my case it would be +/- 2.5 months free). At the end of the month I was billed the full amount again with BIS included yet again. I then called again on 1 April and the person that answered this time round said that she can see that the credit was approved, and this time I actually insisted that they credit the money into my bank account since the credit on my MTN account was clearly not working. She assured me that she had put through the request and that the credit would reflect in my account by Monday 6 April, which it did not. Yesterday I called them and Themba Maqubela assured that he would call me back with an answer around 18h45 when he gets a break,..... I'm still waiting for his call 18 hours later.