Disorganized Service and Bad Attitude

My trip from JHB - HRE was a nightmare. I booked my tickets weeks ago but when I got to the airport the flight was overbooked. The lady at the counter had to phone to get a seat for me and that process took 20 minutes . I was then put on stand-by so I waited. When i got a seat, it was only 10 minutes until the gate closed and I had to check in my luggage, rush to security check, passport control. When I got to the gate the people at the counter saw me but ignored me and left me standing there. When I got back to the counter the lady there told me it was my fault i missed the flight because the other people who were also on standby managed to get into the plane. She said I delayed and that's why I was left behind (even though I had to run straight to the gate. I talked to the supervisor who said that BA isn't at fault. They managed to book me for a flight for the next day but I am so shocked by how I was treated.Your airline was always number 1 in my book but this was an eye opening experience for me.