Booking.slum no refund no reply

I paid for a four-day holiday in Stellenbosch and arrived to find the accommodation very dirty, unkept and unhygienic. I contacted the host to cancel, and he agreed to waive any cancellation fees. I then cancelled the booking on booking.com. I was told that I can expect a full refund in 14 days. It has not been more than a month. It is impossible to get hold of anyone at booking.com. What can be done? Please help!