Volkswagen Dealer's Delayed Refund and Unprofessionalism

I had made an agreement with Tamaş, Istanbul's Volkswagen dealer, to purchase a vehicle, and I promptly made the first payment via EFT. I then made arrangements with a saleswoman for the balance. However, as I was driving to the dealership, they informed me that I needed to pay 75% of the total amount right away. When confronted with this unexpected demand, I decided to cancel the vehicle purchase that day. They informed me that the large sum I had already paid would be refunded within three days and that no one was available to sign for it. Rather than promptly refunding the payment I made that day, it appears they were more interested in keeping our money. I'm filing a complaint against this dealership because of their unprofessional behavior.