I had a problem like this
last year, my number was being given as a doctor's office. Had an even worse version of your problem trying to find out who was giving out the number. People all of a sudden would get totally confused that I was asking them who had given them the number, even *after* I explained 3 times they had called the wrong number and that it wasn't a doctor's office, and that I needed to find out what was going on. Which usually made them immediately want to terminate the call by saying, "Excuse me, bye."
If I actually got them to hang on, they would sound really puzzled and defensive, "No, I don't know if I should give you the number..." Meanwhile, I was freakin' out on the other end of the line, "fer cryin' out loud, just give me the [stupid] number so I can end this..."
"But you want which number?"
(eyes rolling over)