I just realised that I forgot to submit the final version of a paper for a conference, and the deadline just passed last week. What should I do in this case? I contacted the publishing office but they said they are not accepting paper submissions.
You're probably out of luck here. You can try to email one of the conference chairs or whoever might be higher up the chain than the publishing office, but that's a bit of a long shot, especially a week after.
I'm so sorry this happened to you. I've come close to missing a deadline once or twice and I now set days worth of reminders just to be sure I don't mess anything up.