Robbing Peter and, uh, then sending him a bill for it

I got a bill from Beth Israel about 6 months ago for a copay I'd paid at the visit (almost a year before), so I called and asked them about this, and they said it had indeed been paid, and not to worry about it. Then a month later or so, I got a refund check from them for an overpayment on another visit -- something that they had billed me for as not being covered and then which my insurance had decided to cover.

Then today I got a collection notice regarding the first Beth Israel bill. I called and told the person that I had called when I got the first bill and had been told I didn't have a balance. I told him I had gotten a refund check in the meantime, and asked why I got a refund check if I owed them money. He said he didn't know. I asked if there was some other way to look, maybe by pulling up my social, and seeing if they had two accounts for me or something. He said that wouldn't have happened.

He said there was no way I could have gotten a refund check, because it didn't show any refund check. I told him I had definitely gotten one, and I knew this, because a refund check came in the mail. To me. From them. For an overpayment. So he then said "well, I have no way of knowing what's going on with any of this, because you have 12 accounts in here."

Whaaaat? Didn't he just tell me that I didn't have more than one account? So then he tells me that I'd been in the hospital 12 times in the past two years, and so I had 12 accounts. And wasn't he able to pull them all up as being tied to me? I've been the same person and with the same insurance and address the whole time. So anyway, I asked him if he could pull up the fact that they'd issued me a check, since, you know, they wrote me a check, and they'd have a way of pulling that up. He said "that would require me going into your financial record." Wait, because we haven't been in it yet? No WONDER you think I owe you money, yet you're sending me refunds. So I asked him if he could do that. "No, I don't have access to that."