Disgusting service

I booked a flight ticket for the 20th of December I then changed the date and time to the 22nd December cause of unforseen circumstances,so wait for it ,this was the difference in the fare to change the flight R1149 can you believe it,they charged me R714 to change the date and R443 to change the time I am so appauled at this amount and the service I called the call centre twice asking someone to explain me why I had to pay such an exuberant amount but over yesterday and today I was told I will get a call an I did not ,and for the flight I booked on the 20th I already paid R662 so just to change the date and time I paid a further R1149,Mango airlines you disgust me!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!