I have two insurance plans and both specify they are the secondary plan if there is another insurance plan

I (24 yrs old) had surgery and finished physical therapy recently. The company taking care of the billing for my physical therapy sent me a letter stating that both insurances claim they are the secondary insurance and both are refusing to pay my claims. They said I am responsible for the full balance of bills until this insurance question is settled (which they specified I have to do myself).

Insurance A is through my employer aka a college (grad student health insurance)- I am the primary card holder. Insurance B is through my parent- I am a dependent.

Insurance A specifies that they are secondary to all other plans (including medicare) except Medi-Cal, MRMIP, and TRICARE for any services not provided by the student health services. They said in most cases, a plan which covers you as a member pays before a plan which covers you as a dependent. However, insurance A is secondary to all other plans except those listed above.

Insurance B specifies that the coverage under which the patient is the eligible person (rather than a dependent) is primary (that is, full benefits are paid under that program). The other coverage is secondary and only pays any remaining eligible charges.

I listed insurance B as my primary on my bills and insurance A as secondary (I knew the insurance A policy ahead of doctor’s visits but did not know the insurance B policy until a few days ago). I haven’t had issues with other health related charges, but I am also worried they might retroactively deny claims that have been already approved.

How do I navigate this? Is there a way to differentiate whether insurance A or B is my primary insurance?

Thanks,

A stressed out grad student

Also, this is cross-posted in r/legaladvice but I was recommended to post here.