@Damos19 Does Origin actually download the base game and packs, or does it merely verify the existing files? Where do you have the game installed, and did you ever manually move the game files?
@Damos19 Where do you have the game itself installed though? If you're not sure how to find this information, open Applications > Utilities, launch Terminal, and enter this exact command:
find / -type d -name "*The Sims 3*" 2>/dev/null
The command has to be exact, so please copy and paste rather than retyping it. The command will take a while to finish, so please wait until you see the name of your Mac pop up again. Please copy and paste the results into a post here. You can delete your username where you see it—write [username] instead—but please leave the file paths otherwise intact.