question about the medical bill

Hello everyone,

Recently I received a medical bill from a doctor who wants to charge me $150. The reason for that charge is because the hospital called him three months ago. And on that day, my wife was in hospital. My question is : is it reasonable for him to charge me extra fees since my insurance company already paid the hospital? Why my insurance company didn't pay him ? Shall I ignore this bill or should I call this doctor for more information?If I ignore, will that hurt my future credit history?

Sorry I don't have CHinese on computer.

Thank very much for your inputs and sharing.