I got a response from Fairphone support.
It’s fairly disappointing. Basically because my phone works with an esim from another netowork, it’s not a phone issue, and they recommend switching provider.
I understand their response, but it’s really a bummer 
I guess if my provider isn’t responsive, there’s little I or Fairphone can do.
Here’s the response:
Dear Duckle,
Thank you for testing with a SIM card from another operator and providing the results. The good news is that your phone is working correctly with the other SIM, the successful test confirms that your device’s hardware and software are fully functional.
The root cause: carrier compatibility
The issue you’re experiencing is specifically related to your current network operator’s compatibility with Fairphone.
Your options moving forward
-
Switch to a supported operator (recommended) The most reliable, long-term solution is to switch to one of the operators from our VoLTE & VoWi-Fi compatibility list. This ensures full, reliable calling functionality on the 4G network.
-
Continue advocating with your current operator You can request that your operator add Fairphone to their whitelist or manually provision your SIM. While we cannot guarantee success, some operators do respond to customer requests.
I understand this is frustrating, and I’m sorry we cannot offer a more immediate solution. If you have any questions or need help choosing a compatible operator, please let us know.
Have a lovely day!
Kind Regards,