Airtel — unauthorised activity by airtel

We have not purchased any game or wallpaper on our mobile but airtel has one by one deducted rs 80 worth of amount from our phone, sometimes rs 5, sometimes rs 3 and so on again and again. Please arrange to return these amounts or give us a method by which we can stop these things from happening in the future. There is no response from airtel when we call customer care. Airtel must stop this illegal activity immediately.