incorrect price

This is the 2nd complain I'm logging resulting from incorrect price that I have to pay. I did an upgrade in December at took out a contract that costs R149 but mtn is still deducting the previous amount of R268 which is the previous contract premium . I can't contact mtn during the day cos I can't hold for hours as I'm at work and the department that's supposed to rectify the mistake doesn't work after hours . mtn please advise if you don't want me as a client anymore because I can't go through this ever time I upgrade . 1st it was Wonderpark branch now it's Pretoria north . Advise if you would prefer me to port to another service provider because I'm tired really.