Hey Smellbag0_0,
Thanks for the additional context!
It sounds like sometime in 2023, your PSN account was unlinked from the pre-2023 EA account and linked to the current EA account. It is strange that some of your badges and progress were carried over, since game progress and items are stored at the EA account level, and this strangeness might be what live support deemed to be the result of a merge. But ultimately, it was that unintentional unlink that severed your access to those heirlooms and progress.
Since unlinking comes with risks like losing item unlocks, rewards, and progress, there's a chance your heirlooms are gone. However, there's also a chance that the old EA account might still hold your missing items and progress, and regaining access to that account is your best bet. Once you find the email address associated with it, contact live support for help recovering the account. Please avoid unlinking in the meantime until the correct account is located to avoid further data loss.
After recovering the old EA account, check if your progress or heirlooms are in-game. If they aren't, please contact live support again for help with those missing items. It might be worth letting live support know what your gamertag was as well for more context. Unfortunately, the effects of unlinking can be permanent, so if the heirlooms are still missing, I'm afraid there won't be much that can be done if live support says so.