Billing problem

Vodacom send me statement saying that I am owing them a lot of money which according to me it couldn't be true so I asked them to tell me how did that amount come about and they couldn't give me an answer. They have already take me to the lawyers and I also asked them the same thing that how can I pay for something that I have no idea about. So I was hoping that we can resolve this matter in another way because I am really not happy with the way Vodacom did.