billed for service I didn't ask for

I was excited by Mweb's 20gig for R145 and ended up cancelling the service with one ISP. First invoice Mweb billed me for R666.40. Surprised, I complained and was told by arrogant Mweb consultants that it's what I signed up for. I have received a R835 invoice and complained again. Arrogant consultants told me to manage my usage better. Do the expect me to check the usage after each member of my family has been on the Internet? That is ridiculous. I just wanted to pay R145 for 20gig that's all. A disconnection of service beyond that would have been okay. Then I would pay the R145 I signed up for. I want to cancel this as soon as possible or pay only the R145 and no more. While at it credit me back with the amounts over the R145 that were charged to date. My Worst Experience of Bummer (mweb)