I have been a crisis counselor for several months- love it. Was recently offered full time?

I was given a letter of acceptance and have had nothing but raving reviews. The business manager has it out for me and has pulled strings enough to have the offer withdrawn. There are no fulltime positions as hotline counselor until me. I have been getting almost 120 hours every 2 weeks and have been busting my @$$ here. My boss says he is going to the mat for me and I hope he gets it through. I need the insurance and w/ so many hours I need to earn time off as well. Can they withdraw an offer like that if it was not withdrawn for work performance? Have any advice?