MTN charging more than agreed amount

I took a contract with MTN last year December, the catalog clearly states that when I trade in my old device I will be paying R299 per month on Mega Talk/ Gigs S package, however MTN has been deducting R519 from my account, I have gone to the store multiple times and all the consultants were far from helpful, the lady I took the contract from (Lisimelo) has been trying to convince me that R519 is the actual amount that they are supposed to be deducting because she had to add a data deal which is inaccurate because the catalog clearly states that the contract I took is a Mega Talk/ Gig S which means it includes data. She then changed her story and said that there was a misprint in the December catalog and that the actual price is R519 which I find hard belive as I have never received any communication from MTN stating this issue. I then had another gentleman (Wanda) assist me who said yes the issue was with MTN and they are now processing refunds and the difference will be sent to my account, however when I asked for an update as a few months passed without me receiving my refund he also changed his story and said the actual amount I'm supposed to be paying is R519 which again is inaccurate as the catalog clearly states that I should be paying R299. I am highly disappointed in the service that I have received from the MTN consultants, every time I go to the store I am told a different story and I now regret taking a contract with MTN. I am at my wits end and at a point where I want to terminate this contract due to this unprofessionalism but that will cost me even more. I would never recommend anyone to take a contract with MTN, biggest mistake of my life.