I'm really sorry to hear about your plight!
I can barely believe how some women are so incredibly vindictive! Spiteful empty souls, who don't have an ounce of humanity, or compassion towards those they deem as having wronged them. Sad!
Involving the CSA was/is a dumb move because the money you pay goes into a big pot and gets dished out to other mothers of absent fathers. So a proportion of your money is going to strangers' children who's fathers have managed to disappear without paying a penny. Grossly unfair to the fathers of those who want to/ have had to do the right thing for their offspring!
If she'd got a brain, she would have got her lawyer to make you pay her maintenance so your children benefitted solely.
Using the children as a bargaining tool is a really low stunt. You should have as much access as you want!
The law needs to change to make the balance between couple equal and therefore fair.
Perhaps you might want to highlight to her the fact that the more she damages you, the worse it will be for the children (she can't change the fact that you are their dad). Also, one day, the children will be old enough to judge her. She might want to think about that too.
I hope you get you life back on track.