Incorrect amount of debit order and bad service

I upgraded my telkom contract and made changes on the data simcards in July, I was supposed to pay R968,71 for the upgrade and Data simcards however on the 31 July the debit order amount was R1381,81. When I saw the invoice I notified Telkom Northgate and the sales guy who assisted me his name is Lemson. He said he was sorting it out. It is now September and my query is still the same. Now he ignores my calls and never returns my calls. I also received a call from their head office with the 02 number and the lady said she will investigate and get back to me I am stil waiting until today. Telkom Northgate has bad customer service and the sales personnel act as ****mers they only help when they want commission from you when you apply for a contract once you sign and they get paid their commission and there is a problem they don't care. This is unacceptable.