SAA: Unjustified Extra Charges for Ticket Changes!

I initially booked two tickets for December 12th, 2024, at a cost of R5200. Unfortunately, due to unforeseen circumstances, I had to reschedule them to December 20th, for which I paid an additional R1400. Now, after contacting you to change my tickets to April—since traveling on December 20th is no longer possible due to urgent and necessary changes in my leave at work — I'm being told I need to pay an extra R3770 on top of what I've already paid. I was quoted the same additional charge for changes in February, April, and June of next year. This situation is absolutely frustrating, and to make matters worse, I'm unable to get a refund. This is completely unreasonable!