change of airport

The lady by the name of Nonhle Thusi assisted me and explained to me about the query I have. And she gave me a good advise. I booked a flight tickets but I didn't know the airport is Lanseria I thought it was OR Thambo International Airport. I would appreciate if the airline people can explain when we making bookings about the choosing the airport, now I must get off to the airport that I don't know and offline to where I am going. When I booked I saw OR Thambo I don't know where did Lanseria come from. Now when I want to change the airport I must more money is very unfair for customers.