UHC must have conducted an internal audit and changed their decision (I believe they have up to 2 years to do so). The patients will receive updated EOBs from UHC indicating the change, and their responsibily for payment. Unless there is some contractural reason you cannot collect, you should bill the patients. You rendered services and deserve to be paid for your time.
I assume you have patients fill out a registration form and sign something stating they are ultimately responsible for payment if their insurance company denies or does not cover the service.

