FB showing wrong image when sharing/pasting a page URL

If the og:image tag shows the proper image, you've done all you can on your site.

Facebook does cache the Open Graph values for a page though, so when you update them, it can take days (or even weeks) to automatically refresh. You can use the Facebook URL Debug Tool to scan a page and, if you click the "Scrape Now" button, it will re-fetch *and* cache any updates you've made.

Give that a shot to see if the new values show up in their Debug tool. If so, you've done all you can. At that point, it's up to the Facebook algorithms to properly display your content.

I hope that helps,
Alex