Airtel — cheating by not having internet connection even when i have activate internet pack

in the month of February 2011 i activated one day internet pack of 5rs. and on receiving the confirmation message that it is activated i connected my mobile to the internet and started browsing
but after a few minutes i came to know that i had been charged from my balance for the browsing and my balance of rs.75 had come down to rs.0

but wen i checked the internet balance left by dialing *123*10# i had found out that till MB was left in my account
there was no airtel live access point in my mobile so there is no way that i had used that

later i tried to activate the same pack again and access net through my mobile browser for two days and mobile office access point was not getting connected to internet
how come i'm charged for activating the pack but not allowed to use my pack