<prompt> Human: I had two operations last summer JuneJuly at a large state university hospital system. I had paid a few thousand dollars by the end of last September, and I was under the impression that everything was closed and paid for.In June of this year, I got a letter from the hospital saying they had billed my insurance incorrectly and were re-billing everything. I then received a statement a few weeks ago requesting additional payment of around 3k.I do have the money to make the payment in my emergency fund, but I dont feel like I should have to pay if the mistake was on their end.Any advice for how to handle this going forward? Anything I should specifically mention in talking with the billing department?  <response>: Just received a 2000 bill from feb surgery after I already paid 5000 back then. Fun midsummer gift... fight away just make sure it doesnt ruin your credit. 