June 2021
Two days ago I got my account merged with an account that had some Sims 3 packs I was missing. They downloaded and are showing up as installed in Origin but are not being detected by the Sims 3 Launcher itself, so I obviously cannot play with them. Tried repairing my game over 3 times, restarted my computer, cleared Origin's cache and uninstalled/reinstalled Origin but no luck. Because I lost the key codes to these packs somehow I tried the windows registry way of finding the codes
Recover Your Sims Registration Key
But I have no "ergc" folder?
June 2021
@Sims1005363 This is not a case of missing product keys—that would lead to your packs not showing up in Origin either. And you wouldn't be able to re-register the keys anyway. The issue is likely that the packs have been blocked or deactivated: they're still on your accoutn that can't be used. (This is the same thing that happens when someone buys what turns out to be a bad code.) The point is, you'll need to contact EA customer support (again, sorry) to ask someone to look into what went wrong during the merge process. Sims 3 packs are supposed to transfer, so clearly something didn't work as it should have.
https://help.ea.com/en/contact-us/
Be sure to ask specifically about the status of your packs, not just whether they're on your account but whether they're active and valid. If you don't get anywhere with support, please let me know.