There is no way to know for sure whether the use of your dependent's Social Security number is the result of an error during filing, so you should take immediate action to protect your dependent's Social Security number. Call the Federal Trade Commission Identity Theft Hotline at (877) 438-4338 for important information regarding protecting your identity. Then, you will need to call the Social Security Administration at (800) 772-1213 to have them address concerns about your dependent's Social Security number being compromised. Lastly, contact all three credit bureaus; call Equifax at (800) 525-6285, Experian at (888) 397-3742, and TransUnion at (800) 680-7289. Often, these credit agencies can place alerts on credit accounts to prevent your credit rating from being damaged by identity theft. If you have reason to believe that your information was stolen and have information to support it, then you should file a police report along with IRS form 13409. Also, you can call the IRS customer service line at (800) 829-1040 for additional help and suggestions. If your issue is not resolved by calling the IRS general line, then contact the IRS theft protection unit at (800) 908-4490.
Since someone else has already claimed your dependents on their income tax return, you will not be able to file electronically as the e-file system does not allow for duplicate input of Social Security numbers. Thus, you will be required to file your income tax return by mail. You can find all the necessary forms, instructions and publications at the IRS website or you can call (800) TAX-FORMS to order the necessary documents. Include a copy of your dependent's Social Security card with your income tax return when you file. If you filed a police report or completed IRS form 13409, include them as well.
Since the time frame for electronically filed returns is only 10 days and the time frame for mailed returns is six to eight weeks, your return will probably be significantly delayed due to the misuse of your dependent's Social Security number. In addition, the IRS could further delay any refund pending the results of their own internal investigation.
Once you take the steps outlined above, you should receive a response from the IRS regarding the status of your return within 30 days of receipt of your information. You can call the IRS customer service line referenced above to check the status of your return Monday-Friday from 7am until 10pm.