Unsatisfied after date confusion

I am really disappointed after being referred to Travelstart. We booked a ticket, paid for the ticket and then noticed there was a huge mistake on our dates (accidentally chose a date in Jan instead of the same day in Dec). After that we knew we would be subjected to change over fees and were happy to pay standard changing prices and also the difference in flight cost. However, that was not all they wanted us to pay, they have decided that they will charge us R3,300 (this R3,300 will not apply if we went directly through the airline) over and above the R2000 changing fee, the R598 service fee and the R2000 flight cost change as advertised on their website. So instead of us having to pay R4,598 to make the change which is the fair amount, they want us to pay R7,898, and cannot justify the extra R3,300 to me. When asked about the additional amount, we were told that this is just how their system works it out. Even the airline carrier directly has lower fees than Travelstart, why then use Travelstart in the first place? They are supposed to be cheaper than the airlines directly. We tried to adjust this mistake with the airline carrier directly but unfortunately, they cannot make changes on Travelstart's behalf, which now forces us to deal with Travelstart, and deal with their unjustified inflated charges, and no compensation or understanding for the error. Not the service we expected, the airline carrier directly had a very simple and cost-effective solution, but Travel start cannot offer their clients the same. Why then use Travelstart??????? If this is not resolved, we won’t be using Travelstart again, and will make sure everyone we know, is aware of our experience and the way they try and gain extra money from their customers for no valid reason. Really disappointed that such an exciting thing has now turned into a nightmare. I have also seen some other post and complaints and all I can say is that I am horrified at what I have read on the below link, and I am also starting to doubt that the mistake was actually on my side. https://nz.trustpilot.com/review/www.travelstart.com I guess the lesson here is do your research before you use any "cheap" companies.