@shen87 Does it say the content is installed, or just that you own the pack and can download it? Packs sometimes still need to be manually downloaded. Otherwise, try clearing Origin's cache:
https://help.ea.com/en-us/help/faq/clear-cache-to-fix-problems-with-your-games/
Restart your computer, and repair the game in Origin: open your game library, right-click on the Sims 4 icon, and select Repair. Even if you've already done it, repairing specifically after clearing the cache can help shake things loose.
Please launch the game while Origin is online (not in offline mode) at least twice, and if Moschino still doesn't show up at the Main Menu, let me know. Please also go into the Sims 4 installed files, located by default in Program Files (x86)\Origin Games\The Sims 4, and see whether there's a folder labeled SP15. This folder should be inside the Sims 4 folder, not in any subfolder.