I know this thread is old, but hopefully you'll see it! Do NOT press any numbers, just hang up! The numbers don't really mean anything, it just shows them they have an active phone number.
I just got a call too. Same day within 10 minutes of your post. It was a half ring effort that showed missed call. I'm in the same area code so I wonder if they are hoping I will call the number back. I'm on DNC but it seems to mean nothing these days.