Can a employer cancel group policy without notice?

Received notice from hospital that my insurance had been canceled and I was responsible for all the bill.

As part of my pay the company paid all my medical insurance through the company group plan. The insurance company said they did not pay the premium so policy was canceled. I have worked there a long time. The company is a partnership and I have tried several times to reach them but none of my calls have been returned. I did not receive any notification from the employer or the insurance company. What can I do?