Any other way to recover this store items please?

@aodoherty  Try creating a fresh Sims 3 user folder and copying over the DCCache folder, plus ccmerged.package from DCBackup, but nothing else yet.  See whether the items show up in a new save.  The venues won't be usable since you're not moving over their Library files, but that's fine for the purposes of this test.  Please let me know about both regular and premium content.

If none of your content works in the new folder, trash that folder; you're not losing anything since you copied over the files rather than moving them.  Then create another new folder, and this time, copy over a couple of Store items from Downloads and try to install them.  Test a small item or set first, and if it works, try a world.

I will say that with the way that Store encryption works, it's possible you'll need to redownload everything, which would of course be frustrating.  But that's an unfortunate side-effect of the encryption.

@puzzlezaddict

Sorry for the late reply. I tried the both ideas you've suggested but I couldn't fix my issue. I saw all the items in launcher are shown as 'unknown objects'. Finally, I started to redownload and installed everything I needed from the purchased history on the website, and everything installed perfectly.

All the store items looked like this in the launcher. 

Had to redownload from the website to make the items work. Anyway, thank you so much for the help. :D