Breach of contract

I went to Telkom shop on the 06/05/2015 to apply for a Telkom Adsl line, after spending about 30 min in the shop looking at all there deals I decided to take the Telkom do uncapped 2mb line for 395.50 all inclusive, (this I have in writing) today I get a Telkom bill for 1597.90. I phone Telkom logged a dispute with reff number ***8. however how can Telkom want to charge me 583 pm if I signed for 395.50. the consultant that did the dispute told me that if I signed for this that is the amount I should pay and that is the amount I am going to pay per month