A colleague of mine messed something up and I have no intention of helping him fix it.
You don't think it's the kind thing to do?
I don't have to help him. He's not paying me for my service, he can handle it himself
He has to pay you in order to get assistance? Why?
Whenever I've needed help, he's never been there. So I'm not helping him.
You can always do the right thing though. It may be better to simply focus on yourself, and try to do what you know is right despite how the person treated you in the past.