Being charged for Data I do not use

In 20 October 2015 I received September bill from Maintenance Manager in our Company (Micros SA) and I was shocked to find out I have data usage of 400.*** which I then called Vodacom Business department to complain about it and also found out what was accessed and for how long it was accessed.<br> On the 25 November 2015 they emailed me the xls spread sheet which show I was connected 3 times on the internet on 29.09.15 around 2 pm. I then rep**** back to them to say that it is not correct as at that time I was sitting down in the office working on my laptop which has internet access. If I need to access internet I use my laptop. The other thing I have another personal cellphone that I use specifically for accessing internet while I am off duty ,I get 1gig on the phone and it last me for almost a month. How can I use so much data in 2 hrs while 1 gig last me for almost a month. I have asked them to at least tell me which applications or websites have been used and till today I did not get any response . Today I receive another bill for 673.*** data , The worst part is that my phone was on APN setting . I do not use internet on the fone.This is rediculus