Your doctor’s billing office may have tips on what to do (my office used to bill for our older patients)
and try calling the hospital billing office, you’ll find that their angry letters are “routine” and when I did this, they essentially told me not to pay anything and ignore the letters…

another way to keep things quiet is to offer to pay a small amount each month as a gesture of good will…

The trick is not to pay anything until Medicare and the insurance finally get around to paying the bills. Yes, you get a refund…eventually….if you do all the paperwork correctly….

As for harassing phone calls: They are illegal.
Take their name and number, and tell them you will sue if they continue to harass you…

As for billing mistakes: usually a clerical error.
And the error goes both ways (lots of stuff doesn’t get billed for, or underbilled).

Now you know why we docs hate the idea of the government running health care. Insurance is bad, but Medicaid/medicare is worse…