Does the unit your husband goes to have a social worker? Id check with that person, then have him/her check into the bill. Also, I would check and see if you are eligible for some sort of medical assistance. More often than not, there is a "medigap" plan of some sort than can help with these type bills.
The "point" is the procedure was NOT done and they billed Medicare and Medicare paid for "their" share of the first code and the patient is stuck with the second part which, again, never happened. I'd keep calling medicare and ask to speak to a supervisor or go to the hospital billing office and get in their face and threaten going to the local news!