refusal to credit tickets

On the 24th of January, I booked flight tickets for my wife and myself via my phone only to discover after booking that I had had put the wrong dates. I then phone a short while later to rectify my mistake and book on the correct dates. My Edgars account show both ticket payments. The incorrect ticket payment has not been reversed. i have been in contact with Chantel Mclean who refuses to credit my Edgars account because i had made the error and it was not a systems error on their side. on their website they say you can amend your booking and they will charge you and amendment fee. In this case they are charging me for tickets including the amendment fee and refuse to credit the fees charged for the first tickets.