Without knowing specific details, I can only provide a couple of general observations: (1) If the insurer received the premiums from you or your employer, then in most jurisdictions there is coverage by estoppel; and (2) insurance is regulated so that the insurer must comply with the applicable regulations in order to effectively cancel a policy or coverage for an individual under a plan. My first stop would be your boss or employer's human resources office. If your money was taken and no one can straighten it out in HR, you may want to seek advice from a lawyer.
In some form or another, you likely have protection--possibilities include that you are covered by the company, and that you are covered by your employer.
If you can be added back, the easiest solution is probably that your employer puts you back on, and the company agrees to make it retroactive and collect the premiums.
If that can't be done, your employer should likely be covering the cost over your supposed copay.
And if that doesn't work, and you have significant bills, you should see a lawyer--but that's the last resort, not a starting point.