Stuck in Harare because Travelstart booked an unreliable airline

I booked a return ticket from South Africa to Zimbabwe through Travelstart with Fastjet airline. Going was no problem. On Returning l showed up at Harare Airport yesterday 17 Jan 2021 for the 18.00hrs flight only to be told all flights are gone. I had no access to emails and when l eventually got access l saw Travelstart sent me an email advising me of the time change but the departure was still 18.00hrs on the 17th Jan. When l contacted them they said 'We have noted that your ticket has been marked as flown.' How could l possibly have flawn when l got there after the plane had gone? Their last response was we are in contact with the airline at 10.17 am and thereafter they have ignored all emails. I didn't need to monitor my emails because the ticket said nothing about the airline changing times whenever they wanted. I'm stuck in Harare and Travelstart has ignored me. I need to speak to someone in authority so they can get me back home. Can someone from Travelstart call me on +***82