Doctors office billed out-of-network – when to appeal?

I visited a doctor’s office back in December that said UnitedHealthcare was in-network. They ended up billing out-of-network. In February, I called UHC to ask what happened, they spoke with the doctors office and it turns out there were 2 codes that could have been submitted (based on different addresses/offices I think) and they submitted the code that was out of network. UHC said the doctor would be resubmitting the claim as in-network and not to worry. I realize I should have followed up, gotten something in writing etc.

I just got a bill for $400 because the out-of-network claim was processed and approved by UHC. Not sure what happened, so I reached out to the doctor’s office and they told me that due to the claim already being processed and approved by UHC, there was nothing they could do but they would reduce my amount owed to $150 as a courtesy.

My copay should be $25. Is there any recourse here? Moreover, is it worth getting into for $150? Not the end of the world for me but just feels wrong.

Thanks in advance, I’ve read through previous threads similar to this but this doesn’t seem to be an issue of “the doctor is in network but the office is not” – if that was the case, or anything similar to that where I should have done more due-diligence, I would just accept it. I just think it’s an odd scenario. Any thoughts? Is there something I’m missing? Thanks!!