Ex wife refuse to give a copy of 1095A.

My kids have insurance through my job since 2015. I always claim 1 of my kids. This year IRS send a letter saying my son was covered by the marketplace under my ex wife account so I need to send a 1095A form. My ex wife refuse to give me a copy to send to IRS. How can I proceed? IRS will not release my refund until I send the letter, and If I have my kids under my insurance is not illegal that my ex wife put them on a marketplace insurance??