Additional charges for BIS & increase contract

I took a top up contract with MTN in June 2013 for the amount of R209pm for which I have been paying since until in November 2014 they decided to deduct R368pm. I only noticed this end January and decided to give them a call on the 2nd of February. I was told my contract is now R309pm and additional R59pm for BIS which as a Blackberry service. The funny part in this debacle is that I have a Samsung Galaxy S3. I have requested a copy of my contract and they told me that they only keep it for 3 months. I have spoken to 6 call centre agents since the 2nd of February and the only thing I have received after received after every call is a reference number.