If your plan is a "self-funded" benefit plan offered by an employer or bona fide union trust under a union contract, state insurance departments have no jurisdiction. Instead, you may file a complaint with the US Department of Labor Pension and Welfare Benefits Administration at 617-565-9600.
If you are uncertain which type of benefit plan you have i.e., fully insured, self-insured, or self-funded you should contact your human resource department or your insurance carrier for clarification.