Vodacom false sales which led to arrears

I have being using Vodacom ever since I got a phone to date. Other service provider got into the industry and I remained with Vodacom. Guess what they did to reward for my loyalty to date? Vodacom Agent called to sell migration of my three contracts to more affordable and cheaper options. The Agent used that to sell the idea to me, but also indicating that this migration will not change my contracts duration, instead it will save me money. I agreed to that , obviously in this tough economic condition who would not like to save some few rands. To my surprise come end of October all of a sudden I'm in arrears with an amount of around R680, something I have never done before. Upon investigation I picked up that the so called cheaper migration actually added more that R800 to my monthly installment. I used to normally pay R1600, in total monthly. Now all of a sudden I'm expected to pay R2500 to R2800. I would like Vodacom to remove all this additional amounts added on my account because of "false sales" made by one of their Agent. I'm not going to pay for the arear amount I did not create.. My name is now impacted on the credit bureau because of the false sale from Vodacom. Please urgently attend to this matter, otherwise I may as well move myself away from Vodacom after almost 20 yrs with them.