Cellphone Data Charges

I am currently using a samsung S5 on an ANYTIME 200 package which is company issued and since receiving my Samsung S5 in October 2014 i was not overcharged and my data was kept under the limit which is 1GB, on 23 February 2015 my data spiked to 2.8 GB, I went to Autopage to query this, i was told that my current unbilled amount is +R2500 and that i have no content on the phone that could have been using up my data or any downloaded applications that would do this, my service has been soft barred due to the data being used, and still to date after switching off mobile data the data still is getting used up and is now currently on 1GB and rising which will be a charge for the following month Autopage was unable to give me an itemised bill or an explanation as to how the data is being used up daily, please can you look into this as R2500 is a lot of money to be paid for something which i am not using.I use WIFI facilities at work and cannot understand how the data is being used up.