incorrect contract

On the 11th of april 2015 I signed a new contract at autopage zevenwacht mall kuils river. I signed for a vidacom data 500mb special at r69 x 24 months. Nothing additional and I have my signed copy on hand. Ever since then this contract has been a huge mess! It was supposed to be a top up, but I got a call from autopage zevenwacht to say it was loaded inorrectly and was an open line so I had to check the wifi sim each time before using. After this I still needed to go back anyway because the sim was not working. Ever since then I only used it sporadically as I was afraid that I would be charged incorrectly. Since the beginning of may I have stopped using it completely and rather bought data myself. So to my shock, I received an invoice for over r1000 from autopage yesterday, charging me for a 3gig contact with sms's which I did not agree upon. I want them to either null and void this contact or refund the amount already debited last month and to rectify my account. Autopage should take full responsibility for this mess and I am one very unhappy customer who is sitting with a wifi device I am unable to use.