Different booking rules for different people

I wanted to book one night at Sun City Cabanas, but was informed by email that since it was a Friday, I had to book 2 nights in a row, and anyway The Cabanas were fully booked for the Friday night I requested. It was the same story at The Cascades. Subsequently, I found out that someone from the UK booked through "booking.com" for the same night that I was refused. Clearly an overseas visitor receives preferential treatment over an SA resident.