Unfortunately, some people will try to take advantage of the Medicare Part D enrollment process to scam Medicare participants. In this case the person calling you does not work for a Medicare Part D Plan at all. The scams are designed to obtain your personal identification and financial information to steal your money or your identity. There have been reports of scam artists calling from outside of the United States, pretending to be Medicare Representatives or Medicare Part D plan sponsors. Be careful who you trust with your personal information including your social security number, Medicare number, bank account and credit card information.
Medicare has a very informative flier that describes precautions you can take to avoid scams related to Medicare Part D: www.medicare.gov/Publications/Pubs/pdf/11147.pdf