What should I do with an ex-friend who's driving me crazy?!?

My friend and I have been like sisters forever, but now I have new friends, who treats me better, and I think it's time for us to move on. she's usually immature, and bratty, and is usually not a good friend. Any way, we got in a huge fight, during witch she hack my game accounts and stole from me, called me names, and did things I can't just forgive. It ended in us calmly agreeing we were no longer friends. But a few days later, she called and said she missed me. So, we agreed we were not friends, but we would act like cousins. We wouldn't be mean or anything, just not buds. But now she calls me all the time, and acts like everything's fine again! Her other friend is also sort of moving on, so I sort of feel bad for her, but she's driving me crazy! I keep reminding her we aren't friends anymore, but she's clinging on! She still keeps calling, and asking if I want to hang out, it's gotten to where I frequently make excuses not to. What can I do?