You could file an identity theft report with the IRS if you know for a fact that a tax return was fraudulently filed with their SS number on the return as a dependent. Use IRS Form 14039, Identity Theft Affidavit - https://www.irs.gov/pub/irs-pdf/f14039.pdf
IRS website for identity theft information - https://www.irs.gov/newsroom/taxpayer-guide-to-identity-theft
If your e-filed tax return was rejected by the IRS because of another tax return being filed with the SS number and name of your dependent on that tax return, then you will have to print and mail the tax return and include the dependent's information on your tax return. If you are owed a tax refund the IRS will pay the refund.
See this TurboTax support FAQ for the procedure to print a tax return for mailing when using the online editions - https://ttlc.intuit.com/community/printing/help/how-do-i-print-and-mail-my-return-in-turbotax-online...
Within a year the IRS will contact both parties to investigate who was eligible to claim the dependent on their tax return. The loser of the investigation will have to pay back any tax refund plus any penalties and interest owed for improperly claiming the dependent.
When you are contacted by the IRS by mail do not ignore the request made by the IRS for information.
