What are the best resources to help with health insurance denials?

In late 2023, I had hospital expenses outside of the USA, and spent about $3k out of pocket. I submitted the claims to Cigna, but even though I got email confirmations of my submission, it was only until 2024 (when Zoox, the employer who the insurance was through, got involved) that I could see the claims in my Cigna dashboard.

Zoox was initially helpful in getting Cigna to respond to the claims, and they let me know what additional information Cigna needed. Cigna gave inconsistent reasons for why my claims were rejected, including saying that I needed to resubmit due to my plan being 'handled by different department', and that a 'vendor outage... prevented many of [my] claims to come through’. There have also been at least two times that I have talked with Cigna over chat, only to have the chat die after the agent asks for more and more time.

Conversations with Cigna: https://docs.google.com/document/d/1dNDsCJ0_LSed4CmCmkSPQYMA-MpDPL6vg9lVRR1rgOY/edit?usp=sharing

Eventually, Zoox stopped responding as well, though I have a followed up a few times through email.

Is there any way to get Cigna to have a good faith review of my claims? Any government agencies that can help me, or outside companies that can help with the appeal?