Can I sue my insurance agent who told me that my workmans comp policy was set and indeed I did not have one?

I met with my agent in spring of 14 for an hour and a half. Sat in his office filled out paperwork listened to him make the call and left his office feeling I had workman's comp insurance for my company. My old policy had lapsed and had not been renewed for two years. I did not have workman's comp for the two years. I knew it was dangerous so I went to sit with him and make sure I got it set and in place. Months later(9/26) One of my employees got thrown off a horse and is now out. She has a fractured pelvis and herniated disk in her spine. When I was getting ready to bring her to the hospital I called him and he said he would call me back. He called and told me that he had left me a message however my policy had not gone through. I do not believe he ever called me. The bills are now over $15,000 and I do not feel it is fair to be paying these out of pocket. I spoke to someone who said as an agent he acted with negligence by not making sure I had the policy.