Non replacemebt of screen as line comes in the display of screen .

I visited the Samsung service centre to get my mobile phone screen replaced, as a line had appeared on the screen. This replacement should be covered under the warranty. However, the service centre is refusing to replace the screen under warranty, stating that there is a dent present on the phone. The dent they are referring to is very minute and should not be a valid reason to deny the warranty claim. I request Samsung to honour the warranty and replace the screen free of cost as per the warranty terms, without denying the claim over a minor, insignificant dent.