Frustrating processes

I am not a regular traveler, I booked 2 flysafair tickets from durban to east london for dec 2023. Me being someone who does not book flights, I had made a blunder and forgot to add the edgars entertainment discount to the purchase. I contacted flysafair to ask how to add the discount or edit the booking, I was told I can not. I also paid R30 extra per ticket for the privilege of seat changes and cancelations, now that I'm asking if I can get a refund for the tickets and will rebook with the discount included I am being told that I will not be refunded to my account, I will get a voucher and will still be charged R300 per ticket to cancel the tickets. Even so, I am not someone who uses flights so what purpose does the voucher serve to someone who does not use flights and why should I be charged a total of R600 just for that process