iPhone X with 11.1.2

Hi!
Both me and my mom are facing the same problem with our iXpand2 128gb and iPhone 8 / 7 plus.
I tried to fill a format, to get a new one, but it says it need a receipt, which I don’t have for mine since I bought it back in 2015. I only have the receipt for my moms purchase. Does this mean I can’t get a new one? I know which month and year I bought mine. Me and my mom bought it from the same store.

We live in Sweden, so our country is supported.