Incorrect charges

I have been a customer of Cell c for the past 7 years now, I normally pay R700 for my bill every month before I upgraded my contract to a lesser package which started this month. Surprisingly my bill for this month has gone to an amount of R849. I have called the call centre to enquire about this and the lady that I spoke to advised me that they have billed me incorrectly and logged a call for me for charges to removed since I have not gone over my package , she advised me I will be receiving a call back in the next 48 working hours. It has passed 6 working days and I am still waiting for Cellc to get back to me. I will not be calling your call centre because none of your agents knows what they are doing and they could not even give me a straight answer as to why my bill is high. I would like a manager to give me a call back about this and explain to me why you guys are always billing me incorrectly since this is not the first it happens.