it is one thing for an employer to promise you benefits and then later tell you they are not going to provide you with benefits. That is legal because as an at will employee, the employer can change the terms and conditions of your employment, including benefits, at will upon notice to you.
It is another thing altogether to lead the employee to believe he has been given benefits but the employee finds out after the services are rendered that no benefits exist. That is unlawful.
Your facts are not clear which of these exist here. If you filled out paperwork and you had the expectation that you did not have to pay any money to contribute to your insurance premiums, and you therefore thought insurance was in full force and effect based on the employer's conduct and comments, you may well have a claim.
Your claim will probably have to be made under the ERISA statute, which is a federal statute that governs disputes between employees and their employee benefit plans. You will need to find an ERISA attorney to assist you with the claim. It is complicated.
Good luck to you.
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Seems like a miscommunication here as any health provider will ask you for your insurance card right up front and if you did not produce it you were well aware you may be on the hook to pay the bill. That said, they are apparently breaching their duty to get you the insurance? You may well need someone in the legal field to make them abide by the agreement and not then fire you for asking that they comply...
Consider reaching out to your State labor board as well to see if the employer (probably) has violated one or more state labor laws concerning compensation and benefits. This can be done without hiring a lawyer and the employer (if warned in advance of your intent) may see things differently. If they fire you then you can bring an action based on their improper retaliation.
My answer is not intended to be giving legal advice and this topic can be a complex area where the advice of a licensed attorney in your State should be obtained.
Your claim may be governed by Federal Law called "ERISA" which is a complex body of statutes controlling most group helath benefits claims. If the employer is subject to ERISA, the claim that they failed to provide you with the promised benefits is a Breach of Fiduciary Duty claim under the Statute. I would recommend that you consult with an ERISA attorney in your City about this issue. It is likely that if you filled-out paperwork for health insurance benefits and the employer as a plan administrator breached the promise to pay you for these benefits that the company violated either your state's insurance regulations or the consumer fraud regulations or statutes on false and misleading advertising or the rules that insurance companies or companies have to follow. The consumer fraud statutes are often enforced by the State's Atrtorney General's office. The insurance regulations are administered in many states by the Department of Insurance. I would recommend that you contact the Attorney General and Department of Insurance in your state and tell them that you believe the employer/company or the insurance company refused to follow the rules and you want to make a complaint.