Facebook archives all your posts, photos and videos to optical media, not just HDDs. So, when you tell them to delete your content, do they really delete it from its cold-storage system too? Unlikely. Delete Facebook, if you have one, now.
Facebook Posts Deleter 2016 was a User Script that automatically deleted Facebook posts one by one on the FB “Activity Log” page. You could use this script if you did not trust Facebook to delete the content when you choose that option on its page. One FB user, who sued Facebook, found that deleted content continues to reside on Facebook servers on its distributed content delivery network long after the account has been “deleted” by Facebook.