Data Usage Query

I have phoned on more than one occasion. I mailed Autopage page as well. Make no mistake, they did respond but with no info that I requested. My account went from an average of R220 (for almost 2 years) too more than R800 for a month. When I queried this they send me the invoice to show me the amount. I told them that does not help seeing that I need some proof of this supposed high usage on my laptop. I mailed the quesry and twice they have now send the same response. If I use more than my 2 gig I am charged. I understand that - I want to see how they determined that I used that amount of data. Give me the proof please because I do not understand how usage can fluctuate like that. The funny things is that the next month is lower than R200.