Apple India — Manufacturing defect not addressed

My iPhone has a narrow gap between the metal frame and screen out of the box which was not visible and looked normal until dust started collecting into it. I found out there are articles and complaints about the same defect on Apple's community forum. I visited the service centre, the expert there examined and admitted it was a MANUFACTURING DEFECT BY APPLE but he couldn't do anything about it as it will be considered as a cosmetic damage. He also said that a person cannot notice it until dust starts collecting in it. Apple failed to explain why not correctly sealing their product and leaving a gap will be considered as "cosmetic damage", or why would it even be considered as "damage" and not a manufacturing defect. Visited service centre twice, called customer care multiple times but my issue was not resolved and they closed my case. In short, apple admitted it was their mistake but said they cannot do [censored] to rectify it.