MTN overcharge

I upgraded my account at MTN and requested that they give me an account which would reduce my bill which at the time was around R1200. They said if I went onto a different plan it would reduce the bill. My bill has been over R3000 every month ever since - way over what the previous bill was. When I complained to the call center they said they can do nothing about it. I have no idea what I am paying for - there are numerous items which make no sense to me at all. I went in and combined at Waterstone and they said they know that the plan I am on is very expensive and it is not a good plan.