Airtel — airtel data card

I took airtel 6 months plan of 6gb per month in 6k in january. Payment was done in january only. Although i dint use it but that is no issue. The issue is now after 6 months they are sending me further bills without any usage showing outstanding of 1503rs without any permission from me whether i wanted to continue it after 6 months or not. I request airtel to pls deactivate it ([protected]) and since airtel is a respected company i don't except them to charge people without any usage.
Sugandha garg