Mango is ripping us off

Hi All, I booked a flight now and within seconds of submitting the booking realised that i selected the incorrect airport. I called the call centre and was told that I can change this but at a cost. I when ahead to check this cost and to my surprise it was a few rands off from what I paid for the ticket. This is absolutely rediculous. I don't mind paying the difference on the air tickets(about R200), which i think is fair enough but were does all the other costs come from. They are such a huge company but when it comes to customer service and satisfication they suck. Absolutely disappointing Mango.