Making me pay again

On Monday the 28th of September 2015 I was late literally 3 minutes for my flight. I guess late is late, yes, but this was because of some issues I had which was outside of my control. But when I asked whether or not there are seats available on the next flight, they said yes. I asked whether they could place me on that flight with the thought they would help me with this. They then charged me for this flight R1300-00 and when I then asked them why, they simply told me this is my problem and the way it is and they cant help me. I mean there were seats available firstly and secondly just not wanting to help me frustrated me a lot. I was about two years ago more than half an hour late for a flight on BA and they were more than willing to assist and help me. They didn't even charge me a cent. I think this is helping someone all the way through. There were seats available and could just swop my flight. How can these guys (SAA) then not help me. I don't think I will make use of them again. In fact because of this my company will move through to BA again.