They are not supposed to be calling at all if your on the federal DNC period. However, it doesn't stop the illegal ones from doing just that. And yes, they are supposed to place you on a internal DNC when asked also. Charity's, some survey's and political calls are exempt from the DNC and debt collectors have their own set of rules under the FDCPA laws.
ROT, don't answer calls you don't recognize.. And when answered, never give out your information or say yes to anything.
Someone calling for my ex's relative who has never lived with me. I told the guy he had the wrong number, he apologized and hung up. All of the calls that I get asking for him are telemarketers or bill collectors, I'm sure this is no exception.
If you have Caller ID there is no reason to answer calls from numbers that you do not recognize. If it is a legitimate company that needs to contact you then they will leave a message. I do not answer any of these unknown calls and the numbers usually stop calling after a few attempts and most never attempt a call again. I block or call forward the very few that just don't accept that I will not answer unknown calls.