HP India — Overcharged for a service that I even didn't asked for

Address:

SAMTA NAGAR BIKANER

My laptop has been flickering and showing colored screen and some error the service centre changed my window without complete diagnosis of problem and said it will be fine and after that there occurs some problem again.
They have charged 900 rupeess from me for the window which is their mistake not mine because they installed new window without any need as the ultimate problem is of ram.And when i asked now how much will they charge for 8gb ram they said 9800 ruppes . very high charges. I want my money for window back.