Vodafone claiming overusage of data

Location/place: Mumbai

Name of company/service: Vodafone

My bill amounts have shot up from Rs.600 to Rs.3000 over the last two bill cycles. Vodafone is claiming my internet usage has increased which in fact has not. They claim I have used Rs.700 worth of 2G data in two days 4th June till 5th June 2013. And Rs.3000 worth of data from 3rd July till 6th July 2013.
No one has bothered to revert to my complaints despite repeatedly calling customer care and the vodafone store. After repeated follow up on my bill status, I am only told that my usage has increased. I have been using only whatsapp, gmail and facebook on my phone ever since i switched to post paid. No one from vodafone is offering to even provide detailed information on my data usage.