want proof of the contractandusage- credit limits

I have a data contract for R99 a month, In December Cell C debited me an amount of R1378.90. I then called and queried it, I was informed it was data usage. I then asked for a report because I have never gone over my limit and hardly used my device in the month of November and December. I was also informed they gave me a limit of R2000.00 which I was not aware of. How do you give a customer a limit of R2000.00 if they have a contract amounting to R99.00 a month. I then put a Limit of R50.00 on the contract to avoid further costs. January comes and they debit me over R2000.00.I called and asked for a detailed data usage statement as this does not make sense I also asked them to forward me the call where I was advised of a R2000.00 limit on my contract reference number ***(Pearl Molly) on 29 January- she said will take 2-7 working days and till today I have not received any feedback.I spoke to a team leader in customer care Duduluzi Ndolzi- advised that they will get back to me and still nothing. I have reference numbers ***,***,***. I have received calls that they want to send me lawyer letters but how do I pay if I never agreed to R2000