When i worked for a doctor, 100 yrs ago, Medicare did an audit.........we had to prove with the appointment book each visit. If you didn't have 2 appointments set up, then you shouldn't be charged for 2. Talk to the billing SUPERVISOR and if that doesn't work, tell the doctor why you're changing doctors.
Years ago I had a dentist that guaranteed the fillings. Three months later 1 fell out --- he billed my insurance co. for a filling for a different tooth. HAH -- nailed him! I reported him.....Feds stepped in (must have had other complaints) and he got nailed for Medicare fraud, too. He lost his license.
So I stand by my first comment, if you didn't have two appointments, they can't charge for 2.