Airtel — airtel dth scam

I got a new connection from airtel dth. I recharged with 478 rs monthly rental package. After that several times they are changing the package to higher amount. Am getting text of that whenever am again subscribing to 478 rs pack again they are changing it without my knowledge it to higher amount. For that reason my per day rental is getting affected already i losse 2 days of tariff. And its really mental harrasment to change every single time my package to 478 by my own. How can they scam customers like this. I mailed to nodal officer of airtel from west bengal no reply. I called the person who came to fit the connection he got no idea what's going on.