I have never heard of that. Does he owe back child support to you? Could that be what happened they took his refund (it called an offset) for his back child support and it eventually got deposited into your account? This would not have been the IRS that made the deposit, this would have been the child support agency who got the refund (filed an offset) and then deposited into your account.
You need to go ahead and file a return claiming your daughter and mail in to the IRS, disputing his claiming your daughter complete with documentation. If he owes you child support, you still need to claim your daughter to get all the refund you can get. The IRS will go after him to pay them back the erroneous refund he received.
What I am trying to say is if he claimed your daughter, used her exemption in order to get a large refund to pay the back child support, that still is not right. He owes that anyway without claiming your daughter.
If you did not claim your daughter last year (file a paper return) and you are legally entitled to do so, you need to amend your return for 2016 also. Claiming your daughter could result in you getting a nice refund.
I may be totally misunderstanding-so if I am I apologize in advance!
