EOB shows $0 paid on a claim I thought was covered - did I get balanced billed?

Got my Explanation of Benefits yesterday and I genuinely cannot figure out what happened. The total billed was $4,200 for a surgery I had in November. My EOB shows "amount paid: $0" and "patient responsibility: $4,200". My deductible was met months ago and this surgeon is in-network.

I called my insurance and they said the claim was processed correctly but wouldn't explain why I owe the full amount. The billing office at the hospital says they submitted it right. I feel like I'm going in circles and nobody will give me a straight answer.

Could this be a billing code issue? Wrong procedure code? I'm so frustrated I could scream. Any advice on what to do next would be really appreciated.