Wrong billing procedures

I saw an adverti*****t (pamphlet) at MTN's Vaal Mall branch. It advertised an MTN Steppa 7 tablet, with 500 MB of data, for R 90 a month. I took out a contract with MTN on 20 May 2015. <br> <br> I was assured by the sales consultant (Kenneth) that this price included only 500 MB a month.<br> <br> I received an SMS on this tablet on 13/7/15 that said I owed MTN R 1900. I went to the Vaal Mall store to receive a statement, where I was told that the 500 MB was never capped. The data therefore ran over and that was the reason for the high amount. Another sales consultant then capped the data, but could not provide me with any monthly statements.<br> <br> I went to another branch in Vanderbijlpark today(18/7/15), where the sales consultant acknowledged that the mistake was made by MTN not capping the 500 MB . I was also told that my contract was R 99 a month, instead of the original R 90. I did receive 3 months of statements, showing that I only owned R 340. <br> <br> I have to first pay R 3440( (Uncapped data) (5 days after I was told it is R 1900), before MTN will make a call to rectify their mistake. I will also be reimbursed only a month after this call is made. <br> <br> If MTN made the mistake, why should I pay for it?