7 months pregnant and the dad doesn't know

I'm 7 months pregnant and I haven't told the father and i didn't plan on it either. but the other day I was at the gas station getting gas and my ex/baby dad pulled up behind me. he didn't notice my belly right away because I was standing away from him but he said hi to me and so I turned around and said oh wow you're pregnant? I didn't know what to say so I ignored him and got in my car and drove off. now he won't stop blowing up my phone and trying to talk to me, he is even having his friends call me. I dont know what to do. how hard is it to change your number? I don't want them calling me anymore.

I don't want him to know because we never got a long too well and i don't like his family