Contract upgrade turned into nightmare

I upgraded my MTN cell phone contract on January 30th, 2015 but I did not take a handset as the one I have is still working. However, I'm being charged for a handset and MTN can't be bothered to fix my account by removing that off my invoices or to credit me for the amounts I've had to pay over. I've been phoning 3 - 4 times every month to get this sorted out and every time I get told it will take x number of days and it will be fixed and I'll be credited. To date nothing's happened. I get regular SMS's threatening to disconnect my account, which I find upsetting and when I call about it I get a sorry it's not my fault attitude and no help whatsoever. I'm upset with the lack of service and the incompetence I've had to deal with at the call center, which is so bad you can't do anything but laugh about it, my personal favourite being the one that told me that I had used up all my uncapped data.