Booking that needs to be cancelled less than 24hours



We need to urgently cancel a booking for a guest who booked via booking. It is for tomorrow but I cannot find a single phone number for booking.com customer service.


My husband set up our property on booking and synced the calendar  with other websites, but this did not work.


Now we have someone booked that is clashing with another persons holiday.


There is no phone number and the number listed on their website +61 02 9255 9290 is not connected. I am in Sydney, Australia.


Please help me.