Even if you were never on facebook, all it takes is for somebody to post a picture in which they can clearly see your face. That's your unique id. Then they will add more information to your profile gathered not from you, but from your friends.

For sure you have somebody in your group that gave them access, without knowing, to their contacts and your number in in there too, to their pictures and your face and easily recognizable landmarks are in there and so on. You might have a massive profile already all due to the little bits of information your friends are giving away.

Another problem is that the profile only grows larger with time. They never delete anything.