okay, update from my side, for people with the same problem finding this post.
I just chatted with EA help about this and that person fixed something about my game and account, he wasn't saying what exactly, and that I should clear cache in the EA App after that as well as repair my game. I cleared my EA app cache, but didn't repair my game (because that means updating and I haven't updated all my mods yet, the reason I wanted to play offline in the first place) and it worked. So, apparently it wasn't just about clearing the EA App cache, since I already tried that before, but it was about doing so after he changed something what did it.
So in case you haven't tried this, I'd suggest to try this method, in case you can't find the link to chat: https://help.ea.com/nl/solutions/?product=ea-account&category=manage-my-account&topic=login-ea-account
And be sure to add a document, it can just be an empty txt file, otherwise it won't work.