We are calling to 'confirm your appointment' with Dr. Jones. = We are calling to make sure that you will 'keep your appointment' with Dr. Jones.
The museum is open to visitors 'by appointment' only. [=you have to make an appointment to visit the museum]
The court ordered the 'appointment' of an attorney to represent the child.
(..) But you forgot to tell me why the SRPJ department was closed. Why? Half of the French police is looking for me. I call you, make an appointment and you come. Alone. Don't tell me that's because you like me. None at all. What is it then? Damn it! (..)1981 To Kill a Cop