Is it illegal to hold someone back from promotions or transfer within a goverment agency.

I work for the State as a CPS worker for 6 years. Recently there have been a lot of management problems in our office. About 1 year ago they brought in a new Program Manager. She was verbally abusive to me and told me to shut up and to Shut my Pie hole on her first day in the office. I worked on a team of 6 people with a direct supervisor. The abuse I endured was minimal compared to others. We each wrote letters to the Regional Director letting her know what was happening. Instead of talking to us she called us out on the carpet in front of the program Manager. Everyone except me was written up for something within days. I don't know how I avoided it but I did. I just stayed in my corner and tried to do my job. Eventually the Program manager was transfered out. I will never again say things cannot get worse. It is a nightmare. I get physically ill getting ready for work. Nothing I or any of my coworkers do is good enough or right. The entire team has turned over except me. I have been applying for jobs within the agency and have not gotten a lot of interviews but a few. I was finally offered a new position. It was a promotion. I was overjoyed.
Today I got to work and in my email a very short email stating that the offer is rescinded. I asked why and I was told that it was a verbal offer and they needed to check my record and talk with my PM and Supervisor. I went to HR and asked if there was anything in my record that would discourage someone from hiring me. She looked it up and said NO. I have never been written up. I have never been warned. No pips . NOthing. I have always gotten good reviews. There has been an effort to get rid of all of us from that time. I don't know if it is because we are older or because we make more because of our time with the state or if it is simply retalliation for that letter. Of the people who worked on our team a year ago no one will be left. 2 people have been forced into retirement. 1 was put on afterhours (2nd-3rd shift) 1 quit and 3 transferred out early on.

Another thing happened also. A manager from another position I applyed for told HR she wanted me for a job and they told her no they would not be interviewing me because they had other plans for me.