My ex bf keeps calling me with a private number and hanging up when I ask who is at the phone. Why is he doing this?

I was in a very abusive relationship. He put me down/never supported me. Now he is dating a very similar girl, he is very supportive (always liking her photos etc when he never liked me). It’s almost been a year, but he keeps calling me once a week via No Caller ID. He was the love of my life, I broke up with him to see if he would change and appreciate me more but he just moved on and tried to make my life hell (by spreading nast rumors). Why is he trying to call me if he says he hates me so much