Insurance after birth confusion!

I had insurance (Horizon BCBS) through my employer at the time of my child's birth (I was covered by this insurance when I entered the hospital). Two weeks after giving birth, I applied to be added to my partner's health insurance (Aetna) which was then retroactively effective from the date of birth. I expected my employer's insurance to cover the birth and delivery since it was the ACTIVE coverage at the time of admission. My initial insurance told me that I have 30 days to make any changes to “the remainder of the plan/year”. They also told me that me and the baby would be billed under this insurance in the initial post partum phase. My portion of the premium for that month was deducted from my ESL paycheck while I was out in leave. They initially approved it, authorized the hospital stay, and sent me an EOB with everything covered.

However, my former insurance is now attempting to cancel my coverage effective the day before the Qualifying Life Event (birth) and is refusing to pay for the related expenses (going back in what they initially said). Should I contact both insurance companies to coordinate benefits, considering that the employer-provided insurance was the only active policy on the delivery date? I assumed that this would make my employer's insurance the primary coverage and my partner's insurance the secondary. How can my insurance cancel my coverage before the Qualifying Life Event even took place?

submitted by /u/Jaded-Statement-1020
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