Let's touch on some of the issues you raise.
Yes, you can sue the company (new owner doen't matter) for taking insurance premiums and not providing insurance. This is also a federal violation with huge penalties, but it is not easy to get the US Dept. of Labor to look at your case.
Depending on the situation the insurance company should have told you the policy was cancelled. By continuing to collect premium for a policy that didn't exist, you may have an action under the California Insurance Commissioner. Call them, it's free.
Were you doing anything for your employer when the accident occurred?
While the medical providers have a right to go after you for payment, you have several potential actions against your former employer and it likely doesn't matter that he sold the company.