I'm pregnant and my ex calls me out of the blue..what to do?

I think I know what I should do...but I just need that extra reurance. My ex and I have been broken up for 4 months and I'm 6 months pregnant. It's his baby. From the moment we broke up, he ignored every call and text I would send him. After the 4th or 5th time, I gave up completely and stopped trying to reach out to him. I moved on and started to focus on myself and the baby. Not once had he tried to communicate with me. We were together for almost 2 years and I took the break up really hard. Especially because I had just found out I was pregnant again. The first time we got pregnant, we took all the steps to doing the right thing and becoming a family. So it completely caught me off guard for him to act this way. Well, he called 3 days ago and I didn't answer. I didn't feel like he deserved to get ahold of me so easily. I'm not the kind of girl to sit and wait by the phone for anyone. He didn't leave a message which I thought was a little cowardly but it's been 4 months. Now my question is, do I call him back? I gave him a few days to see if he'd call again but he hasn't. I do not want to play his games whatsoever but don't I have to see what he wanted? Like if he has any intention of being involved with the baby? I guess I'm more nervous to answer and him be a total *** to me for no reason. I do not need that in my life. But would someone actual call there ex after months just to be mean? Sorry if all of this sounds confusing...trying to make sense as much as possible. Any responses would be greatly appreciated!