Airtel Telemedia Services - fraudulent deduction by airtel

I AM A AIRTEL PREPAID SUBCRIBER WITH NO. 9760719899. On 1st December I subscribed to Rs.98 Internet pack and since that the sim was used for internet browsing only and not for any phone calls, with the micromax modem.
But strangely on 21st December 2010 when I checked the balance, my
balance is Rs.02. Earlier on 19/12/2010 my balance was around Rs.155/-contacting customer care my number was blocked to 198. I again tried to reason with them from another phone no.9557706541,same thing was done.It is surprising
that when for the whole period from 1/12/10-20/11/10 my SIM was in Airtel micromax USB modem how could I phone or subscribe to some service and my balance of Rs.155/- got deducted.In response Airtel stated that there is no provision of automatic renewal of GPRS package and my balance was deducted for per Kb surfing charges after exhausting my 2GB limit. Now see what happened I was using the Rs.98/- pack on 9557706541 and it was valid upto 20/01/2011 but on this date after exhausting my limit, without my consenting or sending request, Rs.35/- was deducted from my account and I was given 500Mb usage uptill 26/1/2011. On contacting 198, the customer care executive as usual talked in a very ill-mannered way and told that I have myself subscribed to this pack. I told him that this not possible as my SIM is in modem where you cannot subscribe. But he didn't agree and kept insisting his story. My submission is that there is provision for renewing automatically then why original complaint for 9760719899 stands i.e. why couldn't my GPRS package be renewed for 98/-when my balance was more than Rs150/-. Is it not that it was a cheap business practise on part of Airtel to deduct per Kb charges when automatic renewal is a factual practise as is evident above