Auto agent didn't do his due diligence by not changing my request to from excluded driver to included, accident occurred, claim not cover whats rights

An excluded driver on policy was to be changed/added as an included driver, agent didnt do his diligence, accident occurred, claim not cover, what are our rights. Requested agent to add my son on to policy as a new driver. He indicated that my husband now deceased had added my son was on the policy. My son was in process of taking his road test. Could now afford to include him on the policy. The policy was paid in full in March until September 2015 by my husband. I asked the agent to verify his findings cause my husband said he didn't add him on that he did an estimate, he couldn't afford it; If he did it, great, please give me copy. He printed it out and gave me a copy. My son was able to take his test in April 2015. An accident occurred in July 27 and called insurance company and realized that he didn't do his due diligence as my agent nor verified, added or made requested changes. Unfortunately, proof of the copy disapaired.This was 2015 Chevy Trac that was finance w/o the auto dealership verifying proof of insurance.Contract was done with good intention bad faith. Car not being cover. Need help for both issues. Payin for car that down