I had a run-in like that some years back. The insurance was rejecting the bill as a duplicate (it wasn't, the doctor legitimately ordered the test done on three different samples. Two got processed on the same day.) The lab wouldn't just accept the negotiated rate and just kept re-billing without listening to me telling them what they were doing wrong, the insurance wouldn't budge and simply "pay" it ($0 out of their pocket) on my assurance it was legit.

I ended up with the last laugh, though--eventually the insurance rejected it as billed too late, denied, drop it. Instead of collecting the negotiated rate they got $0.