Central Arkansas Auto Brokers of Cabot I put 2000$ on a car and they pocketed my money. I didn't receive credit off of the balance. Cabot Arkansas

I  gave this car lot 2000$ as a down payment on a car that cost 3750$. When I paid my first car note my balance showed 3500$. When I contacted them and asked about it I was told that 2000$ was used to pay my sales tax.  I informed them that there's no sales tax on that car, they stopped answering the phone for me. 

I showed up down there and now the story has changed,  I was told that cash money was used as interest which was never discussed.  Then the owner said "ssince he did an in house finance the price went up to 5750." Which was never discussed.  All of my paperwork says 3750, even the title and bill of sale.  

This man has taken my 2000$ cash and pocketed it, it's like I just gave him the money.  I have all of my paperwork,  he didn't record the cash money anywhere so he doesn't have to file it. I do have a receipt though.  

Can someone please contact me and let me know what I can do.