Nokia India — service centre denying the warranty of phone

Address:

Nokia care, D118 first floor Fateh nagar, New Delhi. (Near Tilak nagar metro station), New Delhi, Delhi

I have a problem with my nokia 6.1 plus phone where the vibration stopped working after upgrade to Android 9 pie. This is clearly software issue and service centre also acknowledged that it will be fixed after software upgrade, but they asked to pay for it even when my phone is under warranty (9 months old, having valid invoice).
When I asked them that it is under warranty then why i have to pay for software upgrade, they said that phone is physically damaged that is why we won't consider it under warranty. And the truth is that phone has 2 very minor physical marks on back glass panel (little more than scratch but not big as a dent)
Basically service centre is finding reasons to charge me for software upgrade of a phone under warranty.
Pathetic service by Nokia, totally lost trust in brand, good products but [censored] customer service.