This is a difficult situation to be in, and I'm sorry you have to deal with it. To start breaking your mom's control over you, you need to stop the 9pm phone calls. Essentially, your mom is bullying you into letting her run your life. The first step is to let her call the police.
I would tell your mom on your next phone call, that you are no longer going to be accepting her 9pm calls more than once a week. You have things to do, and need time to study and her constant interference is breaking your concentration. Let her know that you will be putting your phone on quiet hours at a certain time, and set your phone to allow only certain numbers to break through during those hours. But make sure mom's number isn't one of them! She will threaten to call the police and when she does I would say "go ahead, I'm not doing anything wrong and I'm in no danger." With today's technology, you can also record your phone calls to show the police when they arrive.
I've been in this situation multiple times, but 20 years ago we didn't have the technology we do now and that gives you an advantage. My mom has called campus security and the local police department on me several times, and every time the same thing happened. The police would come, talk to me, make sure I'm ok and leave. It's essentially a wellness check just to make sure you are alive. If you are over 18, they can't do anything to you unless you are doing something illegal. They can't physically remove you from the property or take you to jail. In my experience, they never came into my dorm room or my home or did any type of search. They simply came to my residence and talked to me. They'll then report back to your mom that everything was fine and there's nothing to worry about.
When the police show up, be calm, professional and rational. Let the police know what's going on. Tell them your mom is controlling your life and you are trying to take back that control. Let them know that you told your mom this, and this is the result. Again, be sure to remain rational and unemotional. This is important because the police will be gauging your mental status by the way you explain your situation. If you are completely rational, they will understand that your mom is the one who is being irrational and trying to create drama and wasting their time.
After calling the police numerous times on me, my mom gave up realizing that this scare tactic would not work on me, and she did find other ways to find out about my life like hiring a private investigator. But realize that someone spying on your life like that is not necessarily controlling you. Let them spy, let them see you are happy and living your life the way YOU want to, not the way she wants you to. It's honestly the best way to disconnect from the control and harrassment and settle into your own life.
I would also recommend that you don't go home on breaks. If you normally go home on spring break or the winter holiday break, find a friend that you can spend the time with instead, or if you can, stay on campus. I was lucky, the university that I went to allowed residents to stay on campus during spring break, and I didn't have to go home. This allowed me to further separate from my mom's control and lead to me leaving and getting married.
Summer break may be difficult, but you could get two jobs during the summer to keep yourself busy and out of the house. You could also rent an apartment with a friend and work during the summer which would accomplish the same thing. I'm not sure where you are, but tourist destinations like Disney World are always looking for help during the summer and other busy seasons which is perfect for your situation. You could also take summer classes at your school to allow you to shorten the length of time it takes to get your degree.
Before you do any of this, you'll need to figure out finances. If your mom is paying for your tuition, she'll cut you off when she finds out calling the police won't work. I would research other ways to fund your education and make sure if she does cut you off financially, you are able to continue going to school. This way she can't threaten to cut off funding, you can simply say go ahead, I've got a plan to pay for my education myself.
Ultimately, you have to take back control of your life and determine where you want to go from here. I would recommend doing some soul searching before doing any of this. Figure out what you want for your life, and where you would like to be when you reach 40 and realize you have lived half of your life. That is the problem with a controlling mother. By the time you realize your life is yours, not your mothers and that you can live life without her influence, half of your life is already gone and you only have 40-50 years left. Realize that now, while you are still young and can make your entire life your own.