Forgery is a criminal felony offense, so that's something you would report to the county district attorney (aka state prosecutor's office). Fraud is the civil cause of action, and if you are damaged by the finance department's alleged fraudulent use of your and your spouse's name, then you can sue for the fraud and get damages for any loss suffered.
So, yes, you have a case, but whether or not that case will permit you to completely cancel the sales transaction would require a careful review of the sales contract, the extended warranty, and any finance agreement that you signed. It's a complex analysis for a competent lawyer in your locale -- not something that can be done here at Justanswer.
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