When the doctor's receptionist and MassHealth don't know if Dr. takes MassHealth, what can you do?

Who is ultimately responsible for knowing if a doctor takes MassHealth Standard or not?

Who would likely know if a doctor takes MassHealth Standard or not?

I need to see a specialist and every specialist who CLEARLY takes MassHealth Standard is booked through December already. My insurance ends on December 31 and I found an appointment with the right kind of specialist in the same hospital as my primary care. - Trouble is, I cannot figure out if he takes my insurance or not.

What would you do?