Cheating of Booking.com

Just booked an accomodation for 2 adults, 2 kids, 2 nights on booking.com. Price and dates were confirmed. Final payment in full was done. Unfortunately very unhappy as after payment only 1 adult and 1 kid was confirmed. Contacted the owner of the property but he asked for an additional payment or R1300 to get what I looked and booked for. Cancelled the booking but will never book on booking.com again.