An employer is not prohibited from using an employee's personnel files after the employee is terminated, unless the information is related to the employee's health care records, which must remain confidential per federal law: Title 29 CFR 1630.14(c)(1).
However, what you are describing is the common law tort of "misappropriation of likeness/identity." A plaintiff injured by a defendant's use of plaintiff's identity or likeness can sue for any actual damages sustained, and/or for an injunction to prohibit continued use. The point being that if the employer could not have accessed the information without your access credentials, then you would be entitled to damages. But, if the insurance company would have permitted access, simply by the consulting firm's requesting new credentials, then the consulting firm is not really trading on your goodwill, and you would not have damages.
Hope this helps.
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