If you make yourself a bit more unpredictable, this will excalate the tension for awhile. She will become insecure and redouble her efforts to keep track of your every move.

In this age of cell phones, no one needs to give household members an itinerary of one's day. When you are going out, you can be vague, but offer some reassurance along the lines of "I'll give you a call, Mom, in a few hours and let you know when I'll be home. (or see if she needs anything, or whatever.)"

If she calls your cell phone, delay picking up, especially if you know she is just harassing you. Give her some misinformation now and then. You can always corect it, saying you changed your plans. I'm all for truthfulness with those I love, but not in your case. Your mom will use your truthfulness to keep you tied up. There is absolutely nothing immoral about withholding the truth to protect your right to a reasonable level of privacy and autonomy. A bit of fibbing is just fine too.