I work for Robert Half for over 5 months then was hired permanently with the assignment company I had acrued PTO in which I was told they do not pay out but if I come back I do not lose. I came back a few month later than was hired with a a conversion fee

I worked on a temp assignment last year with Robert Half for over 720 hrs and then was hired permantly. I did not use my acrued PTO. I requested to get paid they stated I cannot get paid for it but can use acrued time if I returned to work for them. I returned 8 months later and my new assignment after a few weeks paid a very expensive conversion fee to permanaently work for them. I again asked for the pto in check as I was not returning to work for them they refused and said they are complying with AZ law? Please advise if this is legal