Value added service activated on airtel prepaid without my consent

Hi, I am using both prepaid and post paid connections from airtel. In pre paid connection, many value added services are actiavted without my consent and everyday rs.10 or rs.20 are getting deducted. I tried to reach the customer care, but I am not able to get through the pre recorded answering machine option and speak to customer care. If I call from my post paid connection, they disconnect the call saying "this is post paid department, we do not handle prepaid queries". How we get to speak to customer executive and resolve our queries. The customer care number - 121 is of no use, only pre recorded messages are being played. And there is no option to contact customer executive. Even if I stop the services, again in next month, new services are activated without my consent. Why do airtel always active the services without customer consent? is there any way to stop this from happening? why are they looting the customers without their knowledge?