Do I need a lawyer to prevent an ex from harassing me for the past year after being told several times to stop calling me for over a year?

I have a past customer that is married. We had a few brief affairs aside from work. I am in a relationship now for the past year. This person will not stop calling me. She calls from several numbers and restricted numbers on my business/ personal phone. She is harassing me continuously. It is unbearable, now. What can I do? I mailed a letter asking her to stop harassing me, she would not accept the certified letter. The police said that they could not do anything. I have too many customers to change my phone number. I do not want her harassing me. She calls and calls my girlfriend names and it goes on and on.......