Packs/DLC No Longer Exist???

Misfit-RX​  Alright, I've talked to one person so far, and he thinks if it's a user side issue, you're looking at an excessively overprotective antivirus (or maybe two running side by side and conflicting), or a connection issue, or a virus.  A connection issue is simple to test on a laptop: take it somewhere with strong wifi you can access, for example work/school or a public library, and repair the game.  For your antivirus, check the Windows security settings to see what you're running.

If you want to check for malware, the first step would be to run a scan using whatever security software you have installed, and then Windows Defender too to be thorough.  For Defender, use this guide, under Current threats > Scan options > Full scan:

https://support.microsoft.com/en-us/windows/virus-and-threat-protection-in-the-windows-security-app-1362f4cd-d71a-b52a-0b66-c2820032b65e

The offline scan in the same section is even better, if you have the patience.

It is of course possible that the problem is on the account side, but neither you nor I would be able to see that.  If EA support hasn't found anything, it's possible that's true, but the issue could also be obscure.  The best way to test that possibility is to install the game on a different device, if you have access to one that runs Windows and is at least able to load Sims 4.  (No need for it to run the game well.)

Barring that, you could borrow the account of a friend or family member to reinstall the game.  Do another clean uninstall first, and nuke the EA App too, so the data associated with your own account is completely removed.  Since Sims 4 is free, it shouldn't be any trouble for someone else to add it to their account.  And while using that account, you should at least see that there are newer packs for you to buy, and their tiles should load properly.