Medicare premiums are not paid out of your pension income (State Teachers Retirement) and are not reported on your Form 1099-R.
Medicare Part A is "free. Premiums for Medicare Part B are either deducted from your Social Security benefits or paid by personal check to the SSA.
You may be paying for a "Medicare supplement" made available through your former employer. A "Medicare supplement" is a third-party insurance policy intended to cover expenses not paid by Medicare Parts A & B. Those premiums would be reported in Box 5 of your 1099-R.
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