Oh, I have more lol. I had a legitimate ER visit for some stitches. At the visit I gave them my insurance, credit card, address, etc... When leaving I asked if there was anything else I owed? Nope.
Fast forward 12 months and I get a letter from collections for ~$500. WTF is this? I never received a bill from the hospital. It took me a bit to even realize where this might be coming from. Once again, this type of stuff annoys me, so I call collections. "It's not much just pay it" - they cut it like $100. Not going to happen. So I wrote them and the hospital asking for the bill details which neither could produce and the delinquent bill was cleared.
I rarely go to any ER type care and I have 2 stories of bills being f'd up. So yeah, the rate of errors seems beyond that of simple mistakes.