Travelstart TERRIBLE customer service

Booked flights from OR Tambo to Cpt and back via Travelstart and have spent the whole week trying to change it to Lanseria on the Flysafair website but the error message continuously says "no flights available for selected date" when there are in actual fact flights available when doing a seperate search for those exact dates. A family member who booked directly via Flysafair and not Travelstart has easily been able to change OR Tambo to Lanseria but I cannot as I booked through this disgrace of a traveling company. I've reached out to customer services over 3 times and their only response was that they unfortunately cannot help with no explanation and assiatnace whatsoever. Definitely don't recommend booking via Travelstart to all South Africans flying domestically, rather go directly to the websites of the carriers and for International flights USE OTHER TRAVELLING AGENCIES, spread this message please. Thank you.