blog pagination

hi there, I’m working with this amazing theme for quite some time now. I stumbled upon a small thing here, my blog posts have pagination so readers see at the bottom of the blog, an arrow with the title of the next (right side) or previous blog (left side). Now…. I cannot remember if this is standard in the theme or I setup a plugin or changed some code…
Anyway I can see posts which I don’t want there. So my blog page has a specific category (blog voor dertigers), but the pagination does shows also other categories, which I don’t want.
Hopefully you can help me out here?
Thank you!

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