No assistance

I just booked flights on [URL Removed] for my parents, however i selected the incorrect time for their return flight. I needed assistance in changing the flight times. I called the call centre and after holding on for 20 minutes someone said they cannot assist i need to pay R280 per passenger change. I had just booked the flight and realised the my error but unfortunately mango cannot assist. the agent then put me on hold again and then cut the call. I tried emailing their enquiries but emails don't go through.