599fashions.com selling items that were already paid for internet California

I purchased several item from 599 Fashions.com. The amount cleared my bank within five minutes. Two days later I recieved an email stating that they sold the dress I had already purchased and asked if I'd like something else. What kind of company sells something out from under a customer? Especially when it' already been paid for? I got my money back, but there is a principle here and I urge others not to waste their time shopping at a site that will turn around and sell your purchases out from under you.