Is it legal for a Used Car company to decline my financing loan, after I have a

signed contract? I bought a Used Car 4 days ago. I signed the contract, so did the manager/owner. I financed it through them. I pay $520/mth for a 5 year loan. I also put $1500 down. I drove the car home and thought it was over. Dealer calls me three days later and says that the loan company can't approve my loan, even after I've signed the contract. They want me to sign a new contract, 4 year loan, $550/month, And have me pay an additional $1000 down. Is this legal? I have the signed contract for the original term, 5 years, $520. I have a temporary DMV card that the car is in my name. Acutally, date sold is 7/14. Thats what the contract shows because I did a phone app before I went up there. Can they repossess my car? Can they NOT approve me, after they already let me drive the car off their lot?

Please help. Desperate. Not sure if they are just trying to Extort more money from me, or if its true. Thanks!