FORCED RETURN TICKET BOOKING BEFORE ALLOWING TO BOARD

Booked a one way flight from India to Johannesburg. When boarding Kenia Airways refused me boarding without giving them proof of return ticket - BUT THEY ONLY ACCEPT RETURN TICKET BOOKED ON KENEY AIR, not with another airline - which I had as that is the only way to enter South Africa. They made me book a return ticket which will now obviously go to waste. This is VERY DISTURBING AND *******ION ON ITS WORSE SCALE.