Shocking Bill

I have a data sim-card with MTN with an iPad bundle, and in the last month of my contract all of a sudden I have a R3200 data bill. When I started my contract with MTN I asked them to put a limit on my contract, and they said it can only be done after 3 months, after 3 months I phoned and was assured that I had put a R1 limit on my contract. I never took much notice of my bill after that and have always paid R350 for my contract. Now I get told on the phone that I have massive data charges in the last month of my contract and that no limit has ever been imposed on my contract. What did the consultant do on the phone then when I asked? How am I supposed to prove a phone conversation that happened 2 years ago. How the heck does this happen? How can MTN write up a contract with someone and then allow them to spend extra money on that contract without phoning me? Especially when the charges are going in thousands!! I've heard horror stories of MTN's billing but I never thought this would happen to me! I'm still waiting for these data charges to be sent me. I'm so extremely disappointed by this service, lies and deception on MTNs part.