I had the same experience with winning a contest sponsored by major banks and credit card companies. Asked me if the address they has was correct and it was. I then said this is a unlisted/blocked phone and they hung up.
I have no clue who these people are. Everytime they call my mom answers it & she asks can she take a message & they wont leave a message. I've called the number back several times & it either rings or gives a busy signal, I have no clue who they are. I'm only 18 & just turned 18 in Feb, so I don't have a credit card, or ANYTHING in my name.