Google indexing non-existent 'category' pages

I have noticed that Google is indexing category archive pages that I’m not using and wondered how to stop these pages from apparently being automatically generated within WordPress.

for example, I have a news section on a site. The news index/landing page is xxx.com/newsroom. I then create pages for each news category in a custom template, use a function to pull stories with specific combinations of tags/categories. These pages have the URL structure xxx.com/newsroom/news-category

Problem is that Google is somehow finding default WordPress category pages — xxx.com/category/news-category. These are not of my making and therefore are not formatted correctly. They are also not included in the Yoast-generated sitemap. How can I prevent these default ‘category’ pages from existing and/or prevent Google from finding them?

I’ve tried deleting the archive.php templates form the theme/child but that doesn’t work. I’ve tweaked Yoast SEO settings every which way I can think of to no avail. Any other suggestions?