I bought my car 3 months back and last week it sho...

I bought my car 3 months back and last week it showed check light engine on. I took it to this place and they mentioned it was due to loose gas cap and it was fixed. Again, on Monday check light was on and I went back narrating my previous experience and also mentioning them that I made sure to tighten the cap after fueling. The rep was rude, adamant and told me that they will charge me if they found out that it was loose gas cap again, ARE THEY REALLY KIDDING ME THAT I WOULD INTENTIONALLY LEAVE IT OPEN AND I HAVE SO MUCH TIME TO COME BACK AND FORTH!! After a couple hours they called back to tell me that there is some other error and I need to contact my insurance. The rep didn't care to explain me thoroughly what is wrong and tried to pin point that it is my mistake and my insurance personnel needs to go and inspect. No choice, I asked my insurance to come and inspect and now they have different versions to the problem. And finally they are asking me to get filler pipe and FUEL TANK to be replaced. I do not understand why it is not covered under WARRANTY since it is a brand new car.
Moreover, in an earlier experience when I went to get my Licence Plate on my car, the rep asked me if I bought my car there and if not they will not do it. I am not at all convinced by their diagnosis and would NEVER EVER RECOMMEND anyone to go to this place.