Apple And Croma — New product purchased shows defaults. apple not providing service

Address: 380059

Website: www.croma.com

I purchased iphone 5s on 14th June, 2016 from Croma retail, Ahmedabad. It suddenly started showing white line on screen. There was no accidental damage or water damage. I went to service center 6th September, 2016. They reverted after 25 days with following response:
"One security screw not open, some kind of white symptoms at upper side on display".
How I am suppose to know about this issue while purchasing device. And is it valid reason from Apple service center.

And croma retail has taken that device with them but YET NOT REVERTED BACK. What am i suppose to do ?

I am paying EMIs every month regularly. What am i doing wrong to deserve such treatment from CROMA or from APPLE.