Getting to their contact section is not easy. Log in on a computer and go to the help center. At the bottom left click on "resolve an issue." For me, it goes to the last place I stayed to try to resolve with that host, but it doesn't matter what appears on that screen, click below where it says "my question is about something else." You'll get a menu of options to choose from. You won't find your particular problem there, but pick which ever seems closest to your problem. I think I went with payout. They will try again to give you some options where you can read more, look at the bottom of the screen again and click "I still need help." At that point you should finally be able to send an email.
I sent a message for this cleaning fee problem and Airbnb tried to call me twice. I wasn't able to pick up and they didn't leave a message. When I called the number back, I was immeditaly on hold. After 5 minutes of waiting I gave up.
For what it's worth, I had a glitch with booking a guest in the past. I sent them a message and got a prompt email response and the problem was fixed. Haven't had the same luck this time.