Airtel — value added service balance deduction

Airtel starts value added services and charged rs 20, though i have not subscribed. I complained and got the refund but they did not gave any reason why was it automatically activated, when i asked them through mail.
I think airtel is scamming people charging for i was lucky i noticed my balance deduction and there was no message receives about the subscription received.

It might be a huge scam of duping people specially the unfortunate people who don't notice and don't know how to get in contact with the customer care.