Renault — Faulty car handed, braking issue since since day of purchase

Purchased kwid rxt car in august 2016 and since the day of purchase facing issue in braking.
Registered complaint almost 100 times and visited service center but no solution, still the issue unsolved.
Company is stubborn and not accepting fault in car as they are unable to find the fault.
20% of the time car brakes dnt work and company has no reason for it.
Everytime i complaint they ask to bring car to service station and do nothing just to fool.
I am writing so that authority can help in finding a solution