Overcharged for 1gb contract

I have been with MTN ever since I can remember and when I did my upgrade to get an iPad I was told it would be R359 per month and not a cent more, I have never ever gone over and was told a limit was set on my account, my bill this month shows I was billed for Packet Switch Data Calls, what the hell is this???? I expect a full refund on all amounts that were overcharged or I will go further legally with this as this is totally unacceptable from such a BIG company, no wonder everyone is moving to the competitors<br> <br> The number is ***