Not enough call centre agents!!!

I have to change my flight schedule for my return flight from CAPE TOWN on the 7th of June,so i have been calling the mango contact number that was given for changing flight schedules since 9 am until now. I have called three times now already only to be told that all agents are busy and my call will be attended to as soon there is a free agent, and i wait for about 7 minutes until i hang up without being helped. This occurred the three different times i called and I still have not been assisted even now. I am trying to change my schedule as soon as possible so that i find space in the other flight i want to change to but this is proving to be difficult because there is no one to attend to my inquiry which is really frustrating.