Return flight not valid when I flew overseas

On March 06 I booked a return flight 2LTS7X from Johannesburg to Miami scheduled to return back to SA on the 16/03/2015 on the 15/03/2015 I had my daughter go to O.R. Tambo airport to change my departing city from Miami to Syracuse New York, she was assisted by a lady called Elli who even printed a confirmation stating that my flight will now be AF2951 when I arrived at the Syracuse airport to check in at the Delta offices routing me to Atlanta they said my flight reservation had been cancelled and I had no booking on that flight. This caused a whole lot of an inconvenience because I had to book a new single trip taking me back to South Africa. My return ticket was cancelled and I couldn't travel as the way I had initially booked. I purchased a new flight under ref H5YW5H I spent an additional R17162.39 and I wished to be reimbursed fully I've been going back n forth to the airport ticketing office n no one wants to take the blame for an error done by Air France. I am very unhappy n disappointed with their service I don't think I'll ever use their airline. I want my money back