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Where should I call if I have other questions about options for paying my Medicare drug plan premiums, or about withholding premiums from my Social Security payment?
If you have any questions about paying your Medicare Part D or Medicare Advantage plan premium, you can contact your Medicare plan's Member Services department. The toll-free telephone number for Member Services is found on your Member ID card or most of your Medicare plan's printed information.
(Source: U.S. Department of Health & Human Services)