WordPress category problem

Hello, I have created different categories on my website, for game, nature, space etc. And the parent category is ”wallpapers” for all categories, but when I click on wallpapers category, it displays the page of game category, the url is wallpapers category but the content is from game content, it should display all content from all the categories on the website, since the wallpapers category is parent for all.

check the link below, you will understand what I mean.
https://www.pixground.com/wallpapers/
https://www.pixground.com/wallpapers/game-wallpapers/

The page I need help with: [log in to see the link]