I recommend that you talk to the employer

find out who is in charge of contacting the insurance company in the administrative office, and ask them to talk to the insurance. Their talk will be more effective than yours.

I had a similar situation. My insurance did not pay the bill for child birth, which was a huge amount. I talked to them several times, they kept saying that I had a second insurance plan. Of course I did not. They just want to find any possible reason to delay the payment I guess. Finally I talked to the people in the office, and thing resolved immediately.