Why is my ex girlfriend being such a *****?

we mutually ended things.. or at least i'm pretty sure it was mutual. it was straightforward on my end at least.. and now she's going out of her way to make me angry. i.e. posting pictures of her and her ex girlfriend before me and sending me rude myspace messages saying how she's completely over me and when i don't answer them she calls me and leaves me rude voicemails saying the same thing. why is she doing this? why can't she just be civil with me and let me live my life? it's very hurtful.