For what it’s worth, you’re not alone. My blog, https://www.juvenall.com, managed to pull in 1,500 trackbacks today alone (more than 3,500 in the last two days). The messages come in large waves over a 30-45 minute period every 6-12 hours.
Now, turning trackbacks off will NOT stop new spam from coming in since unchecking the box simply turns it off on all new posts by default. Old posts, the ones the spam bots go after, will still be hit.
One of the best ways I’ve found to stop this, is to catch a “wave” in the act. When you start getting notifications, jump into phpMyAdmin find the wp_posts table, click on the SQL link and run
UPDATE wp_posts
SET ping_status = “closed”
That will update all your old posts to turn trackbacks off. If you manage to catch it in the act, this *can* stop any more spam from coming in for a while. It seems like the bot will drop your site thinking it’s dead or not accepting the spam.
You can also try installing the Trackback/Pingback Moderation plugin here (though, I’ve not tried it out enough to know how well it works): https://mtdewvirus.com/archives/2005/01/06/wordpress-plugins-trackback-and-pingback-moderation/