Unexplained R4000 account

I upgraded my contract end of Aug from a BB to a Sony. My contract was going to be activated on the 23/09 (as I had changed it) On the 18/09 I receive a sms stating that I have unbilled usage of R3097!!! exclu VAT. I emailed a letter asking to please explain to me what is going on, as in 16 years of being their customer I have NEVER had an account of even R1000. No response just got my phone disconnected, phone customer care on 21/09, lady can't explain to me why my account it so high but in order for me to get connected I need to buy a data bundle, which I did. Still no explanation as why I have such a high account, I was using data and that is that, period. I continue saying it is IMPOSSIBLE there must be something wrong, lady sticks to her word. Yesterday I realise I am disconnected AGAIN, I dare phone customer care, I phone Bfn, tell the lady my problem, she says, Madam your Auto-sync data is ON and that is why your data is sky high, explains to me how to deactivate it. Now currently I still am disconnected cause apparently on the 1/10 will I only be on my new contract. This is day light ******* and clearly your customer care have no clue as to solve a problem! DISGUST