How to permanently delete pages I have already trashed?

On the ‘Page’ admin page, you can search for content inside a page, which might be helpful if you have lots of pages.

But, if you first log in as admin, then go to the URLs that aren’t supposed to be there (but are, assuming they don’t “404”), then you can use the ‘Edit’ button on the Admin bar at the top of the page to edit that page, trashing it. You could also change the status of the page to ‘private’, then trash it.

It may be that people are finding the pages via the googles, so you might consider updating your search XML file. You could also ask the googles to remove the pages from your site’s search results.