Cap on contract mysteriously removed

I upgraded one of my contracts in April 2015 to a 3 gig a month plan at R169.99 with a cap on the contract at that amount. Every month, once I ran out of data, I had to wait till the data would be topped up again or top it up myself if required. In August 2015, I received a bill for the amount of R2001.97 for that contract. I phoned customer service who then told me that I used out of bundle data and that there was no cap on the contract, that is why the amount was so substantial. I spoke to the MTN consultant at my branch and assured me that she did put a cap on the contract. So who removed the cap on the contract? I request a refund from MTN for the difference in the amount and please lead an investigation in order to prevent such problems in the future. ***