Change bookings

I made a mistake while booking as i am from jhb i put jhb -durban instead of durban- jhb i called immediately to Mango call centre to inform them of the mistake i had made and needed to change it i paid R449 for my flight they wanted me to pay an extra R761 on da R449 to change the booking that is ridicules i went on the mango app myself n paid 392 to change my booking that was the extra amount to pay for the difference of prices but i mean why rob us are we not giving them enough business...i should pay R400 extra + call and use my airtime and they charging me to change the booking when i could do it myself and not pay anything extra...i will never use mango again they are ridicules as well as rude mango does not train their staff properly...client services have to be priority for them