You should review the contract carefully and if in doubt hire an attorney to review the contract to protect your best interests. There are statutes of limitations on things like this so act fast.
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Bring the documents to a consumer law/fraud attorney to review. Most will provide a free consultation. This sounds like it could be a classic "yo-yo" deal whether the dealer is trying to pull you back in to get better terms for itself. Did you get an adverse action lender from the bank they claim denied the loan, and does your credit report show they made an inquiry? They cannot force you to sign the new documents. if you are unhappy with the new terms, and they can't find financing under the original terms, they must cancel the contract and return your downpayment and any trade-in (and you must return the car).
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