Billed despite insurance claim being denied with "No patient responsibility"

Hi all, I’m dealing with a frustrating situation with my obgyn’s billing service and could really use some advice on what to do next. I have a post on this under r/personalfinance but thought I might have more luck here. On 7/26/2024, I received a bill from my obgyn’s billing service for $6,223.21 for a service labeled as a “C/S delivery package.” Anthem had denied the billing service’s claim for this, stating “zero patient responsibility,” because they had already approved a similar charge from the hospital. It turns out that the hospital’s bill was for “facility charges,” which included a different doctor (not my obgyn) who checked on me after the delivery.

The billing office sent an appeal to Anthem, to which Anthem did not respond (Anthem claims they don’t have the appeal on file). The bill sent to me mentions “Anthem has not responded [to the appeal] within the required time frame, per California law. Absent their payment, this is your balance.” Also, the bill has no due date.

I’m in California and my insurance is Anthem Blue Cross PPO. The procedure was C-section delivery performed by my obgyn, who has his own practice and is not employed by the hospital. The hospital is his preferred birthing facility and is in-network. The billing service is a vendor located on the other side of the state.

I contacted Anthem and they told me that this issue seems to be due to a procedure code error, because with the way the procedure codes have been submitted by the hospital and my obgyn’s billing service, it looks like I had two deliveries on the same day. They stated that the billing service needs to perform a procedure code review and resend the appeal. However, they also confirmed that the claim was rejected with “zero patient responsibility,” meaning I shouldn’t have been billed. They also tried contacting the billing service but received no response.

I’ve tried reaching out to the billing service multiple times via phone and email to relay what Anthem told me. Their phone number goes straight to voicemail, and despite leaving messages, I’ve received no callback. The one email response I received simply asked if the procedures they billed for seemed correct, to which I confirmed, but I never heard back from them.

I’m concerned about this getting sent to collections. What can I do to prevent this from getting sent to collections and impacting my credit score? What could I do to address the unresponsive billing service?

I appreciate any advice you can share. Thank you!