Because she has cancer, the retired medical office manager qualified for Medicare through Social Security Disability Insurance before turning 65, and she enrolled in a Medicare Advantage plan. She was paying a $385 monthly premium — $4,620 a year — and facing $7,000 a year in out-of-pocket costs, not counting her big prescription drug bills. So last year before her birthday, she called two insurance brokers about switching to traditional Medicare and getting a Medigap plan, which she thought would offer better, cheaper coverage. Medicare rules offer a Medigap open enrollment opportunity for beneficiaries who are experiencing disabilities when they turn 65.