How to get an ex to take a hint?

I have an ex of 3-4 days of her breaking up with me, that will not accept the fact that i dont want her back. She told me when she broke up with me that her life was to hectic and she didn't want to drag me into it. So i took it with stride and got over it quickly. Two days later she wants me back and wont accept that i don't want her and im being harassed. How do i end this problem with out being an udder asshole?