Service non existent with Travelstart

Been e mailing and calling Travelstart for six weeks now to sort out a flight where rerouting has been allowed by the airline.. to no avail. Waited three months to get a reply to confirm this for the ticket and now no response when I’m trying to give them the new date. The service from Travelstart is beyond reprehensible! Cannot do the change through Turkish Airlines as we used the agency and have to do the changes through them. At a loss as what to do next.