Can Back Child Support Be Canceled

My question involves child support in the State of: Maine!

My ex owes me $8000 in back child support. I have joint custody but primary residency. He recently let me know that he was filing to cancel all back child support since he thinks its unfair he should have to pay because I make more. Is this possible and how do I stop him? My son is only there 1-2 days a week, usually just for an overnight..

I have no idea why he thinks he can cancel the back support.

The court likely isn't going to let him do that; wait until you're actually served with something and then let us know so we can try to help you further :)