Baby automatically added to father’s insurance?

My husband and I are both insured by our work. My insurance is better, so when we had our baby in October we automatically added him to it. However, I’ve had a couple bills denied because “insurance isn’t primary” and after calling in it looks like he was automatically added to my husbands insurance for thirty days?

We never requested this and due to the birthday rule his insurance becomes primary…what’s even weirder is that it only applied to like 3 bills, the rest were correctly on mine. I’ve tried calling multiple times and telling them this and there’s nothing they can do as theoretically this plan was active…has anyone successfully dealt with this before?