Hi, I'm scott:
I want to be sure you understand that I'm licensed in California, not Florida; and in any case, lawyers in this forum cannot provide specific legal advice because no lawyer-client relation exists.
Because this vehicle purchase was financed, I'm sorry to say the definitive answer very likely lies somewhere in all that legal red tape of your sales-financing contract!
Often in these complex sales-financing contracts like vehicle financing, there is a provision that the buyers must obtain and insurance. Probably, obtaining insurance is a contingency required by the seller-lender so the company will be assured of recovery on the vehicle in case of accident.
If so, being unable to obtain insurance would fail one of the conditions required to form the contract, and should enable either party to void the contract.
Conditions such as this are waivable, but under the scenario as narrated ("they tell us to show proof of insurance") indicates that condition was expressly not waived by the seller-lender.
Also, while some states have laws requiring vehicle dealers to take back vehicles within 3 days of the purchase for any reason, Florida has no such consumer protection.
I hope this at least provided a little perspective -- if so, I would greatly appreciate a positive rating!