It may be that your sim is somehow autonomously calling the other and inviting them over. It could be a bug. Idk if that is by design or not. You should at least get a notification that they are on their way, though. I searched around EA HQ and couldn't find a post on this. It might be good if you go ahead and post over there. You could have several different things going on. It could be because of the friendship bar, or your sim inviting them autonomously, not getting a notification if the latter is by design.
Hopefully they can get it sorted out quickly. They are pretty good over there, in my experience. Good luck!