Unexpected scratches on the iphone screen.

I have recently started using my iPhone 7 and I use a regular third-party dual layered case whose inner layer is regular silicone, for it.A few days ago, I noticed some clearly visible scratches on the sides of the screen which I not at all expect.It is so because being a student my use of the phone is really moderate and there is no solid cause or reason for my phone undergoing excess of dust or too heavy and rugged use.Furthermore,i seldom take my phone off the case and actually I've never ever used my phone like many of the iPhone users do(i.e without any case or screen protector.).So there is no question of my phone coming in contact with metals like coins or keys and for that i always keep my phone in a separate pocket.So all i want to say is, how can such a well built phone be so unexpectedly poor in resisting scratches due to a simple case?Also the metal body is getting affected due to the same case. That's it.I hope my issue will be looked into at the earliest and we figure out some solution to it.