Why does my iPhone say 7 and not the iPhone 8 Plus that I purchased?

I have a iPhone 8 Plus gold but every time I log into something I get an email that says iPhone 7 logged in. Is this a mistake? Or is it some kind of new update?

8 plus has a glass back. If yours has no glass back than it is a 7 plus

Are you sure it is a 8 Plus?