Follow-up to recent post about Castlevania: Lords of Shadow: Mirror of Fate HD
It was user error.
I was downloading the unlock key without having downloaded the demo to be unlocked. It wasn't in my download list because the demo was never actually on my account prior to redeeming the preorder code when I bought the physical game.
I found the demo on the store, manually because the search function kept freezing, downloaded it, then installed the game. It works fine and is playable.
I apologize to everyone that I argued with, but it still doesn't change my stance that physical game should continue being an option. Sony posted a video years ago when Xbox attempted the same business model of two people sharing their physical disk. It's hypocritical for Sony to take this business model when they made fun of it years ago.
In addition, if I want to purchase a pre-owned copy, borrow a friend's copy, or find a new copy for cheaper at a different retailer, this option won't be available for digital only games; unless an online retailer sells game codes for a cheaper price. But this option doesn't resolve my ability to borrow a friend's copy.
Thank you to everyone that provided troubleshooting steps to find the demo and install the unlock file. You did what the actual Sony agent could not.