Plan-of-Care

We have a plan-of-care from an agency in our area that does not have an NPI, only a license number. They say that they don't bill any insurance company, they bill the patient directly and have the pt take care of sending to the insurance. This patient does have Medicare coverage. If I bill Medicare, I need an NPI. Can anyone tell me if I would bill the pt directly or if there is a way to send the claim to Medicare without an NPI?
Thank you, Ellen