No service from Booking.com about refund.

I booked a plane ticket from South Africa to New Zealand through Booking.com and on Emirates for my son, his wife and two children. We called end of March to move the return date because they wanted to stay longer. We couldn't find another flight through Booking.com for the return flights and was advised by them to cancel and rebook through someone else. We did. We are still waiting for them to pay out the money. We made numerous calls and send email which they didn't even answer. It is a lot of money to throw away, but they seem not to care to support or communicate with us to resolve this problem. Reference number: ***