@nix971 It looks like your post was moved to the Sims 3 section from somewhere else; sorry for the late reply.
Just to clarify, supernatural wouldn't have its own entry in your game library. When you click on the TS3 base game icon, you should see a tab labeled More towards the bottom of the Origin window. Click on it and select Expansion Packs, then scroll down to Supernatural. The button should say Download, instead of Buy like it would for the packs you don't own.
If you don't have the option to download the EP, Origin might have to update your account data. As simple as it sounds, you might only need to quit Origin and restart your computer. If that doesn't work, clear Origin's cache, and if that doesn't work either, uninstall Origin "the hard way." This wouldn't affect your TS3 install.
https://help.ea.com/en-us/help/faq/clear-cache-to-fix-problems-with-your-games/
https://help.ea.com/en-us/help/origin/origin/manually-uninstalling-origin/
If none of these steps help, you'll need to contact EA customer support to find out what happened to your pack—it's possible that you received a bad code. But only a support rep could tell you that, and track down the code if necessary. It would be helpful to have proof of purchase, like a receipt or confirmation email, on hand for the chat.
https://help.ea.com/en/contact-us/
