Angela M. Du Bois, a retired software tester in Durham, North Carolina, wasn’t looking to replace her UnitedHealthcare Medicare Advantage plan. She wasn’t concerned as the Dec. 7 deadline approached for choosing another of the privately run health insurance alternatives to original Medicare. But then something caught her attention: When she went to her doctor last month, she learned that the doctor and the hospital where she works will not accept her insurance next year. Faced with either finding a new doctor or finding a new plan, Du Bois said the decision was easy. “I’m sticking with her bec…