being billed double the contract amount

So i upgraded in October 2015. The personnel from East Rand Telkom did not know weather they had the S6 or not. One says yes the other no. Anyway eventually got the phone and they explained to me about the billing amount for November. Which will be the contract amount and then pro rata from the old contract. But they debited me R553.50 in October and R1042.04 in November. Then December R750.60 and January R757.80. I dont understand why this amounts when my actual contract amount is R399!!! I have contacted the call centre and laid a complaint in January of which im still waiting for someone to get back to me. I've been running in and out the stores since December and no one can give me answers, except that i need to call the contact centre! I am now fed up! It takes atleast 18 to 25 minutes for someone to actually answer the phone when you contact the call centre. What about time wasted every time i need to go into the stores because no one can certainly help me!? I have been getting the same response everyday i send a message, the reply is sorry for the inconvenience. Our mobile team will get back to you.This is ********* & unprofessional! I will never recommend telkom to anyone!