Cemair change flights without consulting with passengers

We are travelling 3rd of December 2022 from Malawi to Johannesburg. We booked through Discovery travel a flight 16:30 to George. Today I logged into Discovery, 2 days before scheduled flight, just to notice that Cemair has changed the flight to 12:35, without consulting us or even sending an email informing us. Physical impossible to land at international arrivals 11:30, go through customs, collect luggage, travel all the way to domestic flights, book in baggage and be in time for 12:35. We made an international call today, 1st of Dec to try and rectify this issue. Consultant told us that Discovery should refund us and then we should make a booking on new flight with different airline. We booked this way in advance, why should we pay more for short notice tickets. She then handed the phone over to the Supervisor, who told us that he will contact some other manager to sort out but we need to stay on the line. 40 minutes on this call, and call was ended by Cemair without any resolution or taking our phone numbers. What now?