Can't use serial code

@19489139839  There's no point in buying a disc tray—if a pack isn't listed in your account, Origin won't authenticate the disc install of that pack or let you play with it.  (This is only for combined disc/Origin installs in Windows.)  As CinderellaGirl91 said, you probably used the code for Seasons already.  If you didn't add it to this Origin account or a previous one, you might have registered it on the Sims 3 store site.  Origin and the store share information, so a code used on one platform will not be usable in the other.

If you still have the code but can't figure out what account Seasons might have been added to, you can contact EA customer support to ask for help.  A support rep can look up the code and the account to which it was added.  As long as you still have access to the email that this second account used, you should be able to ask that your two accounts be merged.  It would also help if you had any proof of purchase (photos of disc, case, and insert; or receipt) to provide.

https://help.ea.com/en/contact-us/

Monte Vista and Hidden Springs need to be downloaded through the store (https://store.thesims3.com/), not Origin.  (Discs won't work either.)  Once you sign into the account in which the content was originally purchased or registered, you can download all of your content from Purchase History, or directly from the product pages.  Again, if you can't find the account that owns this content, you'll need to contact EA support for help.

There is one backdoor way to find out which email address you used to use for the store, if you still have an intact game folder on an old computer.  In Documents\EA\TS3\Downloads, you may see a file labeled [your email].bin, which would be that address.  Then you can use that email to login and get your store content, or ask that it be merged with your newer Origin account.