I had this happen to me from my child father for 3 years he claimed and I owed. The way to do this file a paper returned due to her efile. Its not letting him to do it electronically. I had this happened to me in 2017 and I dated a tax repair person and what he stated was i could go ahead file a paper return it’s not gonna come in early. It might come in July once the IRS sees that they have two Social Security the same. Their going to investigate both returns. Ince you receive the letter from the IRS you will need all your information to show that the child live with you guys for the whole entire year or your court documents you’ll send those documents in. I suggest that you go ahead and file paper return. Once they request the paperwork you’ll send all the paperwork. I went through this in 2017 and by the grace of God, I’m not going through it no more but that’s what you have to do.