@MehoyMinoy8 To be clear, the items you downloaded showed up in the Sims 3 launcher, and you selected them and clicked Install, and the launcher's installer said that it had successfully installed the items? I just want to make sure that everything went as expected up until that point. Let me know if that's not the case.
Otherwise, please delete the five cache files in your user folder and open the game again to see whether the content shows up. These files should be deleted any time you add or remove content, whether cc or mods or even a new expansion or stuff pack. For reference, the files are:
- CASPartCache.package
- compositorCache.package
- scriptCache.package
- simCompositorCache.package
- socialCache.package
If that doesn't help, please let me know whether the files still show up in the launcher's Installed and Downloads tabs; and whether the original files are still in ...The Sims 3 > Downloads. Let me know whether OneDrive is running on this computer as well, even if you never use it.