Overcharge on Contract and Bad Service

I upgraded my contract in Nov 2014 to a Smart S package. I received my phone on the 13/11/14 and the simcard was only activated on the 14/11/14. When I upgraded my contract, I was told by Nelisiwe that the contract instalment was to be R279.00 per month but if I overuse the data, more costs will be incurred. she could not give me a top up package. She then advised that an amount of R289.00 will be debited so that when I reach my data limit, it will stop at that point. I am now being billed for R1921.91 that includes R299.00 Further to that, I was debited for an amount R1421.91 on the 31/12/14. I have since spoken to 3 consultants who have given me 3 different explanations. First being that I overused my data and was being charged from 01/11/14 to the 31/11/2014. How could I have used so much data when the phone was only activated on the 14/11/2014 and mobile data was on for that day only. Thereafter WIFI has been used and mobile data is off. I have requested for a billing account and not received same. I'm not willing to pay for this large without any proofs that the data was overused. I require an urgent response.