Poor Service from Expedia Travel Agent

I was booked on a flight from JHB to Seoul 17 July 2023. Due to the visa application that was not approved I had to make changes at the counter at JHB airport now that I have to depart Expedia Travel is not taking accountability. I am told that I have to pay the full amount which is grossly unfair. What is the reason of making use of the travel agent if they are unable to lead by example. I have been waiting for the costs to pay in order to travel surprisingly the ticket costs now is R21000.00 which is double the cost of the ticket not the difference. I am really annoyed with Expedia the service is poor and no transparency on the processes . Can Expedia attend to this request as it is really unfair