Your game progress is currently saved to the EA account where it was first earned, which is why that appears to have been largely lost after linking your PSN account to a different EA account.
I'm afraid the only way to restore this would be to re-link your PSN back to the original EA account where that progress was made. If you're unable to do this on your end or run into any issues, feel free to contact our support so they can assist.
The article below has some extra details in addition to what's mentioned when going through the unlinking process, and I've attached some relevant info below as well.
Unlink your platform accounts from your EA Account
When you unlink a platform account from your EA Account, you can link it to another EA Account, but your in-game progress will not transfer over.
That means you’ll permanently lose access to all of the following:
- games and game progress
- DLC, expansions, and anything extra you have for your game
- memberships and subscriptions
- in-game purchases.
If you unlink your platform account and link it back to your original EA Account, you may be able to get access to your stuff if you still can access the account.
Do you play Apex?
If you unlink a platform account that you use to play Apex Legends, you may have issues with Battle Pass leveling, item unlocks, and other errors.
Instead of unlinking and relinking a platform account you play Apex on, it may be better to start fresh on a new account.