I'm curious - do you know why they are calling you in for an interview repeatedly when they have no position? Is there some kind of quota where they have to have people come into the office to make it look like they are doing something? Do they reinterview people every year? It does sound really weird to me that this is the *third* time they have you come in. They should know by now whether they want to work with you, why are they wasting your time?