made an offer of 31500 for a truck then they tried adding my down payment on top of that for 35500 total financed and scamming me until i caught it in the paperwork

I made the mistake of buying a car from here a few weeks ago. I was told I was getting 5 thousand for my trade in. They told me 5 thousand and after I got my paperwork they only gave me 4 thoursand. I