Airtel — wrong information and then that causes damage on your pocket

Address:

New Delhi, Delhi, 110030

I have got the internet mifi connect couple of month back. The dealer gave me with the offer of 3+1 month offer and i paid the amount in advance i. E. 4995 inr and they told me that after 4 month it will get automatically renewed. But now they are charging 4500 inr per month from me. This is sheer loot with customers. I don't know from where i can complain about this.
One can't expect this kind of behavior from a company like airtel.

Can somebody help me in this.

[protected]@gmail.com is my e-mail id