CemAir let me know 2 hours before the new departure time that my flight is departing 2 hours earlier, without providing any good reason for this

CemAir let me know 2 hours before the new departure time that my flight is departing 2 hours earlier, without providing any good reason for this. I had to reschedule important client meetings and attempt a mad rush from Pretoria to Johannesburg to make it in time. Other passengers have similar stories and one doctor had to postpone critical patient engagements. This unreliability of the schedule is unacceptable. The only reason for not just one star is that their aircraft staff is friendly and the onboard snacks and drinks are generous.