Airtel — Fraudulent charges on prepaid number

Address:

Karnataka

My cell number is [protected]. I suddenly find my account was siphoned off approx Rs. 200. I did not understand how but I added additional Rs. 300 charge to continue using the phone and found that it was also depleting without me making any calls. So I got worried and turned my phone off but that did not stop my account from depleting and I found that all Rs. 300 gone in one week that I could not even make 121 operator call from that phone. So I called operator from other phone and found that somehow I got signed up for GPRS service, me or any member of family did not do it. And the service is such that that keeping my phone off does not stop the charge from occurring, I also can't stop service from my phone, your 121 operator is refusing to stop the service - he wants me to call up another number for that. So I have following questions:
1. How did I land up signing for service that I did not ask for or needed?
2. What kind of service is this that keeps charging even when the phone is off?
3. Why can't I get to remove this service, either from my phone or operator?
Currently my only option is to throw the sim and sign up for new service with another operator but I feel you people need to give my money back.