Double Monthly Charges

Last month I received a bill for R1133 for the month, this month I suddenly receive a bill for R2133. This is unacceptable! When phoning the Customer Support I was told that they cannot do anything for me and I need to take it up with the branch. I was also told that I was being billed for Pro Rata rates, but when I did the contract I was told that I will only be liable for my monthly contract cost which was R549 for my Galaxy Note 4 and R399 for my Sony Xperia Z3. When I do simple math it should only be R950 every month but now all of a sudden I have to pay R2133. When logging a complaint about this it seems that I have to take matters in to my own hands as the Customer Service does not want to get involved with a branch upgrade. Can someone please sort this out for me as I am not going to pay this due to a branch or Head Office error. Please get this fixed or please cancel my contract as I also had issues with not getting my data and SMS's for 2 months. I cannot believe the level of service I am getting, this is truly unacceptable. This must be sorted out before my debit order date or must I will cancel the debit order?