The most likely answer is, I'm afraid, that you've been hacked. I'd suggest you urgently check your settings, especially bank account details, and try giving Airbnb a call on 0203 318 1111. I find they usually pick up the phone while messages don't get the speedy response I'm looking for.
Change your password for a start, maybe contact any guests you've got booked in and let them know (I'm sure they'll understand). While I'd always recommend using the Airbnb platform for messages, you might want to give them a mobile number for now?