Kulala Flight Change and Call Centre nightmare

I made a booking online for the the 27th of September 2019 but because of some urgent piece of work we have to change our flight date to the 26th. I called the Kulula to make change 2 months in advance and I was told it's possible to change my flight without any additional costs. While in the process of doing that I got cut off and thought maybe they will return my call but that didn't happen. On the 25th of July I wrote and email, the representative called me back saying I need to pay like R1300 to get my date changed. Thats a *******, we only leaving in September. This is really unacceptable!!!