Without a photo/screenshot, it's very difficult to diagnose the problem. That said, SAA's site is notoriously difficult to work with - often requiring numerous attempts and using another browser (e.g., I often have to use Safari rather than my fairly locked-down Firefox).

You say you're booking from the US. Call the SAA call centre in the USA +1 800 722 9675 They're usually pretty helpful. If you have the screen up with the fare and details, they might be able to help you book or continue the booking.