What can I do if my former employer is calling and sending me emails and text messages?

My former employer (a dentist) won’t leave me alone. Since I quit he has constantly sent me text messages, emails and even phone calls with his disgruntled theories that I am to blame for some of his patients leaving his practice, that I never told him about his patient's inquiries regarding their treatment, that I never collected payments on outstanding accounts, that I was not loyal to him, and the list goes on. First, let me begin by, I started in January 2013, the treatment I and other employees endured was very uncomfortable and clearly hostile. This employer would make comments to us regarding our race, our choice to have kids, our 'incompetence' (in not so many words), and the President of the United States, and he always somehow managed to accuse us (his employees) of something, without proof. I quit (just like everyone else before me) because I had had enough. That was the day that he was complaining about how he was going to do payroll. Mind you, a few of the previous employees and my checks had either already bounced or we were not able to cash it (this was not the first time). After I left, I got a lot of text messages, phone calls, voice mails, and emails from my former employer. He made it clear that he was very upset and not liking that I left. That I put him in a situation he'd never been in. (No employees they had all quit! I was the only one left.) He had a habit of scheduling patients at 9:00 am for a 3-4 hour procedure and not show up until 9:30 or 10:00 sometimes 10:30 and after the patient had been there waiting that long the doctor would come in, check the x-ray and send them on their way without treating them because he had reasons for not doing the treatment. (There are too many reasons to list) When Patients would be upset. When he did treatment, he would numb the patient, and then leave the office to go to his house or go get breakfast and leave me and his dental assistant to care for the patient.