COB Retroactively Denied Claims

I live and attend a university in California where you are automatically enrolled in health insurance if you do not waive it. Around October/November 2022, I visited the on campus health center regularly due to an ongoing reproductive issue. The nurse gave me a referral to visit the hospital near campus that is covered by the university’s insurance. I completed my visit and received an initial EOB that covered the majority of the total.

In the beginning of 2023, I was reading through the policy statements for the university insurance , and it stated it is always the secondary to other insurance. I immediately asked my parents about their insurance and I called the university insurance to provide them with my primary insurance’s information. The person on the phone submitted the form on my behalf.

In July 2023, I received a balance from a debt collector for this date of services (two claims). I checked the status of my claims through the portal and the reasoning stated they cannot work on it until they know what the primary paid and they have asked the doctor to send that information.

Long story short, I am now dealing with this issue with both insurances. My provider sent the claims to my primary insurance which was denied for timely filing. However, my provider did not initially send proof of timely filing so they sent that now as well. The appeal is in process, but even if it is not denied for timely filing, my primary insurance will most likely not cover because it was out of network and not an emergency.

I am writing a letter for my appeal process. Is there anything I should mention in this letter to help my case with the primary or is it more appropriate to mention it to the secondary once it begins their process with them?