You should contact an attorney who specializes in consumer law, and have them review your paperwork. Most, including my law firm, will provide a free consultation. A good place to find one if the National Association of Consumer Attorney's website: naca.net. It is possible that the Truth in Lending Act along with state laws such as the Consumer Fraud Act or the state law governing installment sale contracts have been violated in this transaction, but an attorney will need to review the documents to give you an answer. Even if the financing is not yet in place when you leave a dealer, you should be given a copy of the contract with the required disclosures of the financing terms. If the dealer is unable to obtain financing on those terms, he is required to return your downpayment and trade-in (and you would have to return the car in a normal sale transaction), unless you agree to different terms. They are not allowed to simply force new terms on you, without your agreement. You should never sign blank documents at a car dealer, no matter how trustworthy they claim to be, and you should always leave with a copy of all of the documents. If you believe you have been defrauded by a car dealer, you should also consider filing a complaint with the Illinois Attorney General's consumer division.
Your situation is too involved for an online answer.
Using the written documentation you have is a good place to begin. Contact a local lawyer - many may give you a short free consultation - to discuss your specifics. Far too many variables exist in the short post you wrote for any further observation by me. Many attorneys have information posted here on Avvo.
You might find my Legal Guide helpful "How to Choose A Lawyer For You"
You might find my Legal Guide helpful " What Do I Tell My Lawyer"
No one can know what the record is in the case because online we cannot see your documents. You need a lawyer. Check with a lawyer in your locale to discuss more of the details.
Good luck to you.
NOTE: This observation is made available by the lawyer for educational purposes only. This observation is not like a communication with a lawyer with whom you have an attorney-client relationship along with all the privileges that relationship provides.