I complain to human resources how about a write-up for my manager he then started to micromanage me

I'm a truck driver. I went to a company to pick up a load the shipping clerk called me the n-word I told her supervisor put it in writing she admitted calling me the n-word and her supervisor sign my statement I then told my manager about it. Later that day the company called my manager and complained about what happened. So he wrote me up and I went to human resources to complain about the write-up. He then began to micromanage me, get me home late, and reduce my salary significantly. He also searches and micromanages me to look for reasons not to pay me, he has also sent me home early when I told him in writing that I don't want to go home and I'm still available to work. They'll send me home to have a reason not to pay me. I had a phone conversation with him that supposedly on a recorded line and I asked him why are you treating me like this is it because I went to human resources. He said yeah I didn't appreciate you going to human resources about me it offended me because I feel I did nothing wrong. Am I being retaliated against? Do I have a case for retaliation? Also I live in Massachusetts but the trucking company I drive for is out of Pennsylvania where do I file my complaint?