@clairecoffee I can't help with the missing packs; you'll need to go back to support and ask them to re-add your content. (If this doesn't work, please let me know.) But just to make sure, please clear Origin's cache:
https://help.ea.com/en-us/help/faq/clear-cache-to-fix-problems-with-your-games/
restart your computer, open Origin, click on the Sims 3 icon, select More > Expansion Packs, scroll down to Late Night, and see whether you can download it. Do the same for High-End Loft Stuff. It's possible the packs are still on your account, and forcing Origin to refresh its data will make them available again.
When you create a new Sims 3 user data folder, you don't need to delete the old folder. The point is to install store content into a clean folder, with no interference from anything else. Then you can copy over your saves, saved households and builds, and anything else you want to keep. Here's a complete list of the files in that folder, so you know what to copy over and what to ignore:
https://sims3.crinrict.com/en/2011/01/faq-user-files.html
However, it's possible that the saves that you played while Late Night and HELS were installed won't open now that those packs are gone, or else they'll open but be corrupt. So it might be better to wait to try to play those saves until you have the packs installed again.
@clairecoffee Screenshots of the errors would be great. I'm not sure why tech support couldn't or wouldn't add your packs back into your account; it shouldn't work like that.
Error Screenshot 1
