Can a provider send a bill to collections if my EOB says I don’t owe anything?

I truly can’t figure out what to do here. I have been getting bills from Natera for over a year now for $649 for genetic testing. My EOB says my responsibility is $0 – my understanding from taking to my insurance company is because Natera failed to get prior auth.

I have sent Natera my EOB multiple times, I have repeatedly confirmed with me insurance that I shouldn’t have to pay anything, yet Natera continues to send bills and has been threatening for months now to send to collections.

I even had an hour long conference call between my insurance and Natera, where my insurance explained why I shouldn’t owe. The Natera billing rep agreed, said they would cancel the charges and forward me confirmation – which I never received. The bills continued to come and when I called back they said they had no record of that phone call, and just tried to convince me to go on a payment plan. Every time I call they just say it doesn’t matter what my EOB says and I need to pay.

I have no idea who else to contact to resolve this and feel like I’ve run out of options.