What I'm gathering from this is that you registered your Steam-bought games through thesims3.com, and then created an Origin account (not realizing you already had one from registering at thesims3.com) to buy the two new packs. Is this correct?
If so, you may be able to log in to Origin using your thesims3.com credentials and install your Steam-bought games from there, then log in to the "new" Origin account and install the two new packs from there. There's no way, as far as I know, to install the new packs into your Steam version, since Steam and Origin don't play nicely. Otherwise, you may need to contact EA/Origin support and ask if they'll transfer the games from the "new" account over to the account that already has your base game and other packs, and then install the whole shebang from your "old" account.
Make sense?