Change contract without permission

In August 2015 I received a call from one of MTN'S telesales people to upgrade my phone. I said I want to upgrade my phone but the lady insisted that I must also upgrade my internet contract. I told her I have an uncapped service and do not want a different contract to which she rep**** that it is exactly the same contract, but I should upgrade my simcard of the internet as that will cost me less in a month. I never upgraded this service for many years now and although the monthly fee increased as I am working month to month, I never had a problem as I had my uncapped service.<br> So, under the false information that it is exactly the same contract, I said it is fine then. However, not even a week after, they cut my internet service and phone line off as I reached my limit! I explained to the customer service that I have an uncapped and they said that my contract was upgraded to a 2GB not uncapped service and they can do nothing about it.<br> Our local MTN office helped me to change the contract back, but I still have an account of R5395.98 on my internet which MTN do not credit. How can this be? They **** to me and gave me false information and now I must pay for it.