We have no idea which one of your dependents were claimed as a dependent on someone else's tax return and the IRS will not tell you. Usually an ex-spouse is suspect, but in other situations it is due to identity theft. In a situation such as yours, where someone else has already filed a tax return either claiming your dependent(s) or using them to file a fraudulent tax return, the IRS will not let you Efile your tax return. The reason for this is because someone has already used their social security number(s). The only option available would be for you to paper-file your tax return. To do this, you would select Paper-File instead of Efile when you are in the File stage of completing your return. Then print, sign, date and mail your tax return by April 18, 2017. The IRS will probably investigate who really should be getting the deduction. If you would like to call the IRS and report this, their number is 1 (800) 829-1040, but they probably will tell you exactly what I have told you.
