Why Not Refunds When You Cannot Use It??

I tried to make  an online  reservations for a flight to Chicago using my debit card. The information said I had to give more information. So I assumed the processes would not be used . Since the flight did not suite my schedule, I  tried another reservation. The following day I noticed that they had reserve two flights for me and charge my debet card twice. Now they refuse to refund one of of my money. And are keeping my money. They come up with some type of excuse for not refunding.  This is not right. How can they stead fast and not refund some of my money. The flights are at the same time and I cannot use it. This is not right.