Hyundai N1 city ridiculous after market service

In 2021 my sister Jessica Adams bought a brand new Hyuandai i20 from Hyundai N1 city. On 10K km the car started misfiring intermittently she took the car to Hyundai N1 city, they told her unfortunately they can't pick up anything based on there evaluation there's nothing wrong with the car. 2nd and the 3rd time same story. The 4th time she took a video with which they then had no choice but to acknowledge their incompetence. They took the car into their workshop and advised her that they replaced the coil packs which I doubt happened as a week later the car still misfires. The car is still misfiring and at this point we dont know what to do anymore as we not getting any help from Hyundai N1 city. She currently works in healthcare and this is her only means of transport into a very risky area. Her contact details are Jessica Adams ***.