Best to wait for a message if you don't recognize a number. If you answer, they still make money by listing your number as ACTIVE and selling it to telemarketing companies. A lot of times they call randomly via number generators. Everyone gets called eventually. I was just called by this number as well which led me here.
Just got a call. Same thing, I let it ring, they left no message. But, here's the kicker, when you try to call it back, it says to try your call again, as if it's not an existing number!!! WOW!