boyfriend and I broke up

My boyfriend and I broke up and I initiated the break up, we argued and then we both said we're done with each other and also said bye. Now he keeps messaging me and arguing with me about my Snapchat story, he also  told me to tell  my friend not to screen shot his story and we got into an arguement about that, we both said bye to each other so why does he keep messaging me if he told me he doesn't care about me ?