I'm not going to give my parents money
Why aren't you going to get them money?
I don't want to be so obliged. I'm stopping all contact with them.
Even though your parents may need help, you are right to not ruin yourself financially for their sake. You are an adult and have to take care of yourself now, so you can't give them money that you need to live. I wouldn't cut them off completely, though, because they're still you're parents.
I gave them money when I was in high school and I don't owe them anything
That's a completely reasonable position to take. If you've already helped them out financially, then it's your right to not help them out any more.