When the IRS receives two separate tax returns using the same Social Security number (SSN), it will result in the second one being rejected. If you believe someone may have fraudulently filed a return using your SSN, then you should take the following actions.
What to Do After a Fraudulent Return
For cases of potential identity theft, the IRS directs you to use IRS Form 14039. This officially lets the IRS know that your information has been compromised due to another return being filed with your SSN.
Form 14039 will ask for your information, the tax year that was affected, and the last return you filed prior to the identity theft. The completed form should then be mailed along with a copy of your Social Security card and driver’s license (or another government-issued identification card if you don't have a driver’s license).
After reviewing your Form 14039, you may receive a response from the IRS called Letter 5071C. This will include instructions for verifying your identity which can be done over the phone. Note that the IRS will never initiate contact with taxpayers directly. Therefore, if someone tries to contact you, then it will most likely be a scam.
Since it was your SSN used for the fraudulent return, you can request a copy using IRS Form 4506-F. This will help determine if any other family information such as a dependent’s SSN may also be at risk.
Meanwhile, you should take steps to ensure more damage hasn't been done. Check your credit reports and consider freezing your accounts. Also, file reports with the police and the Federal Trade Commission (FTC).
You Must Still Pay Your Taxes
Even if you suspect you're the victim of identity theft, the IRS says you're still responsible for paying your taxes and filing a tax return. Therefore, print your 1040 and mail a payment for how much you believe is owed.
For more information, please refer to the IRS Taxpayer Guide to Identity Theft.