No Feedback on promised credit after 4 months and 10 calls

MWeb supp**** a defective Ethernet cable with their modem. Immediately after my account was activated, notified them that I was having connectivity issues, packet loss and the service was unacceptable. The sales agent, Brett Whyburd, promised to credit me until it was resolved. After 6 months of sweat and tears on my part Telkom were called and they explained that the Ethernet Cable MWEB supp**** was the issues. We swapped this out and the problem was resolved. I discovered that MWeb had billed me for those 6 months and only given me credit for the first. I've contacted them on multiple occasions explaining that they owe me credit. The operator always promises that Brett will call me by the end of the day and now 4 months later I still haven't received a call or my credit. It's clear they have no intention of calling me back.