How can one report fraud when the check never comes in the mail?

Approximately 4.2 million Medicare summary notices -- or paper forms that summarize processed claims -- were reported as "undeliverable" to beneficiaries in 2012, according to the Centers for Medicare and Medicaid Services inspector general.

CMS relies on beneficiaries to report any suspicious activity on their notices — but if they never get those notices, fraud can go undetected.

A total of $3.9 million in checks to beneficiaries were returned, with 26,266 undelivered notices in 2012, according to the report.

"There continues to be a problem with incorrectly populated beneficiary addresses in the data systems that claims processors use to process MSNs," the IG report found.

CMS also struggles to track and followup with the notices, the IG found.

The agency's financial report for 2011 alerted CMS of this problem, yet the issue has gone unfixed.