This is a ripoff and unreasonable treatment

I changed the flight date on my ticket this morning, and made a mistake on the date, by 1 day, initial call made at 8:29am spoke to consultant for 16mins, after call, immediately got confirmation email and realize date was 30th and not 29th. I called back less than a minute of receiving emails, to fix the MISTAKE, call made 8:47am. I was not even sure whether the mistake was made by me or the agent. The request was made to correct this and have date the 29th, not the 30th. Call was ended, got called back 12:52pm,saying that I needed to pay an additional R600 to just correct a Mistake made, which I made, as per call. So in total I paid R1500 for a change of booking dates, including a mistake which was corrected within 1 minute of notice. This is pathetic, and to top it all off, you won't give me my money back, so was forced to pay this amount. This is a ripoff. Are you telling me that, if I request a change and make a mistake and within 1 minute of noticing and waiting in queue for 5mins and then waiting another 4 hours, not my faults, that I seriously have to pay another R600? This didn't even impact your service, or seating or space in the flight in any way, as the changes was made within ONE MINUTE OF REALIZING IT AND AN ADDITIONAL R600 LATER FOR A MISTAKE. WOW