Health Insurance Denial Help!

Hello there, I just got a 1k+ bill from Sutter saying my insurance, Anthem EPO did not pay for the claim as it was out-of-network.

I searched on the Anthem website, and the facility I visited is in fact in-network. Also the doctor is in-network but at a different address few miles away. She just works for Sutter at two locations.

What are my options here? I want to call tomorrow to dispute the denial, and I want to be prepared.

Thanks!