No,you can't get reimbursed for Medicare premium. I believe that besides the Medicare card, the approval letter, or award letter for disability discusses Medicare eligibility, so they will not let you get reimbursed because they will say with all that documentation they sent, you should have known. Also, If he did try to cancel Medicare, he would face some serious penalties once he tried to get it later down the line. I don't know the exact amount, but I believe it is a 10% penalty for each year. So lets say he cancels his Medicare for 10 years, once he does go on it he would have to pay 100% more for his premium, and who knows what the premium will be by then, but he'd be paying twice as much for the rest of his life. My recommendation would be to cancel his coverage through your work, and have him use his Medicare coverage. Or have him enroll (only during open enrollment) for a Medicare Advantage plan.