VRBO/booking.com calendar synching not working-need urgent help with double-booking for tomorrow!

Hi all,

I have a bit of an urgent situation. I just received a reservation on booking .com for TOMORROW, but we already have VRBO guests staying in the house for the next two nights. We DO have our calendars synched with VRBO and it clearly shows the dates are unavailable on VRBO. And we've had this set up for a year and have never had a calendar conflict, even with a 90% occupancy rate, so something has definitely broken.

I already reached out to the person that made the booking. com reservation to let them know I can't honor their booking and why, but I can't find any way of reaching anyone at booking. com for their help. This double-booking isn't my fault, as everything is set up as it should be, so I shouldn't be charged for a cancellation, if that's what I end up needing to do. Does anyone know how to reach booking. com customer service? Like a real live person? Thanks advance for any help you guys can provide!