Closed boarding gate

On the 30th September 2017, my daughter flew from Capetown International to ORT with FLYSAFAIR. Her flight was at 15:40, we arrived on the dot 15:00. The person at the check-in informed her that the gate is closed and that she can not board the plane, she claimed that we were late and that she has to board 40 min before takeoff. Went to the kiosk where I had to pay an additional R600, 00 for a seat on the next flight. I think it is ridiculous that I had to pay for a next flight while her plane was still there. I am of the opinion that it is all a huge racket, no customer loyalty towards this company from here on for me. I used to fly only FLYSAFAIR. No more. On top of that, they told her that her luggage was too big and that she has to check it at another gate. All the while it's the same backpack that she came on with no such restrictions.