I am so angry at Coral Springs Automall right now!...

I am so angry at Coral Springs Automall right now! Almost a month ago, I bought a Mustang from them. During the course of the sale I was clear on the money's down and the payments that I could afford! I even put down more than I wanted to because I was told that was the only way to complete the sale. I drove the car off the lot that day, switched tag and insurance, signing papers from the bank that was to fund me, and thinking that it was a done deal! I even came back ro give them 6 months worth of bank statements, since I just got another job making more money. Still, I thought it was a done deal. Almost 3 weeks later, I received a message from AJ, in finance, telling me that the bank that I signed the papers with, would not fund me, and we needed to go with another bank. I also had to give them $500 more, or bring the car back! This isn't how you do business! Why was I allowed to drive the car off the lot, and drive it for almost 3 weeks if it wasn't a done deal? I don't have the extra $500, and I feel it was Coral Springs Automall's mistake, and THEY need to make good with me, the customer! They took all of the joy and pleasure of getting a new car from me! I am so disappointed!