Looking through your Address Book you may find that you have multiple records for the same doctor. It's possible that these are separate records for this doctor to cover different details they may have. For example, if the doctor works at multiple clinics, has multiple provider numbers or receives their correspondence via multiple different pathways.
If the records are exactly the same and there is no reason that there should be multiple records, then you may wish to mark one as Inactive by opening the record and selecting the Inactive checkbox.