I wpuldn't be happy either. I think in Indiana at least one person involved in the call must know that it is being recorded. And as you said, the calls can only come from this one ad, and on top of that they have you filling out a spread sheet... I think something smells rotten . just my opinion. Maybe call your local wage and hour and see if they can answer the question, is it legal what they are doing ?
GOOD LUCK