Donix135 Sorry for the late reply. If the game works through Steam, you can use Steam rather than the EA App and also access your DLC. Once the game is installed, open your App game library, click Sims 4 > Manage > Manage add-ons, then download the packs listed there, but NOT a second copy of the base game. The DLC should install and load just as it would if you owned it through Steam. You'd need to uninstall the EA App version in order to download your packs again.
If you do want to try again with the EA App, uninstall the game through the App if you haven't already, clear the EA App's cache (again):
https://help.ea.com/en-us/help/faq/clear-cache-to-fix-problems-with-your-games/
Restart your computer, and create a new folder into which you'll (try to) install Sims 4. The folder should be on the root level of the drive of your choice, for example C:\Games is fine, but not C:\Program Files\Games. The folder can be called whatever you want as long as it's not "The Sims 4."