They are saying that he didn’t sign up for it in 2022 and he did. It came directly out of his paycheck

If they took it out of his pay check they have to honor it or his employer can be sued.
Every insurance agent that enrolls employees in life insurance and other insurance is required to record the conversation if it is a virtual enrollment which most are since covid or obtain a wet signature in person, and inked signature.
If they took it out of his check then he signed up for a policy and there was one or the company would not have been billed and it would not have come out of his check.

If they took it out of his check then it was most likely on a group cafeteria plan that could only be changed once per year.

Do you have proof it was taken out of her check?
Who said she was not covered? employer or insurance company?

Her dad had the policy on her and our son since 2019 through the company he works for offers

If they were taking it out of his check then someone is responsible, legally.
Whether it is the employer or the insurance company. Just saying.
You need to gather your proof.

It is through guardian life Insurance

Get together what evidence you have physically like what was the policy supposed to be term life? Juvenile Whole life? from their HR or web site. then check stubs. How old was she?
And then Dm me. I am no lawyer but I can tell you about insurance and whats what.