It’s very unusual for top coats to lose adhesion, with modern paint processes. That’s not to say it’s impossible. New cars can sometimes get covertly repaired before delivery as well. A paint depth gauge can check this out. Proving this is of course another thing.
It is also an area where disputes can drag on forever.
If you feel strongly that it is a paint fault and MG say no, then I would recommend that you get a written paint specialists report.
There are a few issues here. One is professional reports are not cheap to get, depending on the paint issue it might be better and cheaper to just pay to get it put right.
There is of course the other issue that if it is a defect causing paint to lift it’s unlikely that it will be isolated to just a small spot.
Good Luck.