Claim processed as Out of Network despite provider being marked In Network on my patient portal, customer representative said they could not re-process the claim. What can I do?

I (24F) recently had a post-op visit for a surgery that took place in December 2022 (Located in Seattle). The surgery occurred on my old insurance but since this post-op was in January, it was under my new insurance plan (both were Aetna).

I searched in my patient portal beforehand to ensure the doctor was in-network on my new plan and found that both her, and the facilities, were marked in network on my plan in the portal. My visit occurred at an outpatient facility for a larger university hospital system and I expected to only pay my copay (which they always bill after the fact and not at the appointment).

When I saw the claim processed I was on the hook for the entire bill because it was processed as out-of network. I sent a message in the portal including screenshots demonstrating the in-network status, and the claim was denied when processed as in-network. I called the customer service department and the rep said that he also saw it as in-network in my portal but couldn’t do anything because their claims team said the hospital was out of network. He said my only recourse was to file an appeal.

Is there anything else I can do to fight this? I plan to mail in my appeal but don’t have much hope that they will correct this mistake despite all of my information coming from the insurance provider themselves. Do I have any rights in this situation?