The FTC has issued a warning about fraud using the name of the Do Not Call List/Registry. At first the caller is seemingly helpful offering to put you on the Do Not Call Registry. The FTC says just hang up.
The commission reports these are not coming from the agency or the registry, but for callers phishing for information.
In fact, there are only two ways to "de-register."
Also, ignore any email going around claiming your Do Not Call registration will expire. Once registered, a phone number remains there permanently unless you remove it yourself. Be sure to report each and every call you get that violates the list. The FTC can fine offenders thousands of dollars per call.