is receipt needed for iphone replacement?

i have a factory problem with my iphone.

the apple support here in Albania said it was a factory fault but even if i am entiteled to a replacement, they won't replace it if i don't give them them original purchase receipt which i don't have.

why do they need it if they see it in the system that it is still in warranty and that i am entiteled to a replacement?

Please inform me what to do as i can not find the receipt. does this mean that i'm stuck with a non working iphone? or just they are not enough informed because i don't see why do they need the receipt if they can check in their system that i'm within warranty.