Fly safari Bad service and bad planning

I booked a flight to Cape Town in July, for the 21st September 2018,paid for it and got a confirmation for the 13h40 flight ,today on the 21st September as I'm supposed to travel I get told that the flight was overbooked and I'm on standby for the next flight which they are also not sure I will be accommodated, the worst thing is their staff who doesn't seem to care or understand that we book flights at specific times because we have made other arrangements on the other side.Im still sitting at OR Tambo being told that the flight that I'm on standby for is delayed for an hour. This was my first time booking on this airline and it will be my last. As if things cannot be worse, we are told that we have to pay for the change of flight as if it's our fault. Bad service at its best