Why do I get these Nationwide calls when I have no credit card?

I don't have a credit card nor have I ever opened a credit card. But for the past few months, I have been getting one or two calls a day from about three different numbers. Sometimes they leave messages; half are automated, and they all ask for someone (not me) about their debt. One message even read "by answering this call, you agree that you are Eric and are responsible..." and then I hung up. I am starting to get fed up, so I did a directory search on these numbers and found out these are all different lines that Nationwide uses to go after credit card debtors (at least from what I've read about these numbers). What?? I don't even have nor have I ever had a credit card! How do I stop this and is there a way to prevent these people from ever calling me? How is my number even in a database for this?