The answer may not be as simple as the question. Where I would start is looking at the contract. Presumably the employer has a written plan that you paid into. If so, there should be a written plan with rules regarding its purpose and uses.
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The answer depends entirely on the circumstance under which the employer received the money, and for what. If this was a flex plan, you would not receive a refund, but the details of the payment are not mentioned.
This comment is general in nature and is not intended as legal advice. It does not create an attorney client relationship and obviously is not confidential. You should contact an attorney in your area who can review with you all of the relevant facts and give you specific legal advice.