Unable to contact Booking.com by phone in New Zealand

I have been trying to contact Booking.com in NZ for over half and hour.  I am continually cut off.

Also have tried to email.   Very difficult to email Booking.com

I wish to cancel a booking for today as this particular client has had a no show for the third time since October. As the booking is for today I am unable to cancel on line.   I have sent messages to this client Phone and tx to no avail.