Airtel — VAS deduction

I am using an Airtel Mobile Campus SIM. The thing is Rs. 1.50 is deducted from my balance for VAS Download. I dont know what thsi VAS Download is. I havnt download anything from the Airtel service. I have talk with the customer care also, they didnt give any exact reply instead they say we dont know about the VAS download. More than 10 times this amount (Rs. 1.50) is deducted from my balance. Anything to stop this... will be very thankful if someone give me the clue to stop this