Overcharged on Account - Extremely upset customer

I recently took out a smartdata contract with CellC at the head office in woodmead which is a special that was on for R399 per month with the Huawei E5577 lte Mifi Router. I just got my invoice saying that the amount I owe them is R1195.04 and is due to come off my bank account on my billing date. I am extremely upset at this especially with me being a new contract holder with them.it was confirmed by the consultant that assisted me at the head office that my exact and correct monthly premium is R399. The correct amount that should be debited for November 2015 is R506.41 which is including my pro-rata amount for 8days from 24th October to 31 October 2015. I contacted the call center and was advised by the consultant that she can see on system that my contractual amount is in fact only R399 a month and she agreed that the amount billed to me is extremely incorrect, however all she can do is log an enquiry with the accounts department and that feedback will be provided to me within 2 working days. The Ref# is *** however I cannot wait 2 working days as my bill date is the 25th. I need this issue rectified as a matter of urgency before the debit order run on 25th November 2015!