#I want my refund

I made an online booking on the British Airways website for a return flight (BA 6419) from Johannesburg to Cape Town, 03 Jan, 1:50 - 4pm. I got to O.R Tambo international airport at 1pm, only to be told that they can't check me in for the flight, and the next available flight was 5pm, with a penalty charge of R1300. I had to book with another airline.