Explanation of account

September 2014 a lady contacted me from ALtech Autopage telling me that I qualifies for a upgrade on my data stick. She explained to me that my monthly amount will be R90.99. and that will be the fixed amount deducted from my bank account. I specifically asked her that this amount will be staying the same and that if the data is finished that it must be a topup. She confirmed that the monthly amount will be every month R90.99 and that if the data is finished it will be cut off. For more than a year and a half my account was R90.99 and suddenly from February when everything has been changed to MTN now for the first time I receive a account of R798.38. I phoned Customer Services get a reference nr: ***. When I phoned again this morning the 29th of March 2016 the guy at Altech Autopage customer services informed me that this is the right amount and that if I had a problem I must phone MTN. That is unacceptable. I will not pay that amount. I do not have a contract with MTN, my contract was with Altech Augopage.