Nelson Mazda lies, and renegotiation on an already signed contract Antioch Tennessee

I went to the dealership to look at a '03 mazdaspeed protege and possibly test drive it. the salesman was a nice guy not to pushy or anything but i told him i wanted to put 400 as adown payment he say that would be fine i also said i was look at paying 200-210 a month.Well i had to wait about an hour or so for fianancing to come through. He came back and ask if i could put 1000 down my payments would be about 320. i agreed and sign for that amount

I finally had to go to the fiancing part and the guy said it would be 350 a month and i agreed and sign all the paperwork. the next day i receive a phone call from the fiancing guy and he said i had to put more money down or put a co-signer. so i asked to put more money down, then he said no i have to have a cosigner just to keep the payments the way they are. but i thought when you sign a contract it law biding i guess i was wrong,

i'll update to let know what i have to do

Andrew
smyrna, Tennessee
U.S.A.