Volume button falling off phone S8 phone under warranty

I have a Samsung S8 Smartphone which is less than a year old. I acquired the phone in Feb 2019. I keep the phone in a cover and when I took the cover off this week, the volume button fell off. Samsung says that the volume button is not covered by the warranty. I am really dissappointed that they cannot cover the volume button that broke off whilst the phone was in a samsung protective cover.