I think you may have allowed Facebook to allow other Facebook users to search for your profile via your number. Can you check my earlier comment at https://news.ycombinator.com/item?id=26712835 and let us know whether or not this is/was the case?

> "Facebook Settings > Privacy > How people can find and contact you > Who can look you up using the phone number you provided?"

Is/was it set to "Everyone"?