al6xis The only thing I can think of at the moment is to do another clean uninstall and reinstall of the game, but this time, create a new admin Windows account when you're reinstalling, AND create a new Steam library in which you'll install Sims 4.
If this doesn't help, I'll keep trying, but it might be easier to get a refund from EA rather than pursuing this issue further. Sims 4 DLC isn't eligible for automatic refunds, but if you contact EA customer support and say you've never been able to use the content (and you can link this thread as a reference), support may be willing to issue a refund.
You'd need to talk to a real person, in real time, for this to work. If you don't see the live chat option, try a slightly different category of issue. When I choose Sims 4 > [all topics] > I need help loading my game, I see live chat under some help articles.
Like I said, I can keep trying, but I don't want to waste more of your time if nothing is going to work. You can try buying C&D from Steam rather than EA next time, and wait for a sale if it's more convenient. Steam has Sims 4 sales about as frequently as EA, although not always at exactly the same times.