He filed his tax return and added my son to his tax return when he wasn’t supposed to add my son as his dependent. He father hasn’t lived with him never
That happens when two parents (or others) claim the same child on a tax return. The IRS is now trying to sort out which one of you was the custodial parent who had the right to claim the child. It sounds like that is you, so you need to provide the proof that the IRS needs --- here is a link to some of the information that may help you to show the IRS that the child lived with you.
WAYS TO PROVE TO THE IRS THE CHILD LIVED WITH YOU
https://www.irs.gov/pub/irs-pdf/f14815.pdf
One of the ways to prevent this in the future---get an IP PIN for your child
That happens when two parents (or others) claim the same child on a tax return. The IRS is now trying to sort out which one of you was the custodial parent who had the right to claim the child. It sounds like that is you, so you need to provide the proof that the IRS needs --- here is a link to some of the information that may help you to show the IRS that the child lived with you.
WAYS TO PROVE TO THE IRS THE CHILD LIVED WITH YOU
https://www.irs.gov/pub/irs-pdf/f14815.pdf
One of the ways to prevent this in the future---get an IP PIN for your child