Complain against consumer loan

Location/place: Hyderabad

Name of company/service: Bajaj finance service

I have taken a consumer loan for purcahsing a Refrigirator and AC, and when I am about to pay the Bajan finance service person who was in the showroom (Aadhiswar electronics) gave me an option for 0% intrest loan, which was confirmed by the showroom manager. Now I have been charged 321 rupees extra and when I am trying to contact no body is answering and no phone numbers are provided in the website or anywhere else. I dont know whom to contact and how to get this issue sorted out. I even visited the same showroom where I bought the equipement from and no body is responsisble over there. Please help