The letter was sent to inform the debtor that the refund check sent did not repay the entire debt due Medicare.
What the letter means
Additional money is due the Medicare program.
A check should be sent to the MSPRC for the "total amount due" as quoted in the letter. If you have previously mailed a payment you will receive a letter acknowledging that payment has been applied to the debt and further advise you of any debt owed to Medicare. If a refund is due you will receive a check in a subsequent mailing.