Travelstart is useless

This is the second time I have been struggling to get hold of Travelstart to change flights. I have been trying to change a flight booked for four of my co-workers since Friday 2021 at 09:50. They came back to me about the flight from East London, but up till now, no feedback on the other three that must fly from Port Elizabeth tomorrow 3 January 2022. I have tried using the app, I have tried online, no feedback. This is unacceptable, because we paid exstra for the flexi tickets, but now we cannot get hold of them. The flight ref is ZA***7. This is the worst service I have received from any travel agent.