Why is my old FWB still contacting me?

Back in 2009, I had met this guy and we we went on a couple of dates and we ended up just being FWB's for about a year off-and-on. If I had began a relationship, casual sex between me and my FWB was ended. However, in November I had cut him off for good via text. We were friends on Facebook and I found out that he had a girlfriend. He knew that my number one rule was not to be sexually involved with someone in a committed relationship. We were also having unprotected sexual contact and I was nauseated that he would he disrespect his relationship that way. So I abruptly ended things and told him that I wished for him to NEVER UNDER ANY CIRCUMSTANCES contact me again. For about two months, he said absolutely nothing and things were great. Then I started to receive those late night phone calls from him again. I haven't answered them and he keeps calling. How come he doesn't get it?
Why is my old FWB still contacting me?
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