Rotten Mango

Booked a flight from Johannesburg to Durban. Departure time 17:45, to arrive in Durban at 19:00. Then n receive a message just stating that the flight has been changed to departure 20:45 arriving 22:00. So all my plans for the evening is gone. On asking my money back, to book on another airline, they refuse, just offering a voucher. Will never use Mango again, hope they go in business rescue and close forever