Amarithana It sounds like you've signed into a different account than the one you used to purchase the original content or register the codes. Even if you're sure you didn't, the fact that the content isn't in your game library is pretty clear.
To find that account, or what happened to your content if it somehow disappeared from this account, you'll need to contact EA customer support. Finding the codes is relatively simple if the game is still installed on your old computer.
Windows: https://sims3.crinrict.com/en/2013/09/how-to-find-your-serial-number.html
macOS: https://bluebellflora.com/finding-your-serial-key-using-terminal/
For support itself, I would strongly suggest using the live chat option rather than email. If you don't see it, try this link:
Make sure you're signed into an EA site (this one is fine) before clicking the link and that the location in the lower-right corner of the browser window is set to U.S. or U.K.
Alternately, try using the help site without being signed in. Some categories of issue allow you to proceed without an active login, and many of those offer the live chat option.
