Could it be a scam? If it’s a phone call, or an email, then absolutely, it’s a scam. However, if it’s a letter, then it may be legitimate. Make sure though that you check the content against the content on the IRS website, and make sure that you are using the IRS website to verify your identity and not a website that looks like the IRS. If you have one, you may want to consult an accountant.
There are more and more identity theft refund scams where people make up bogus tax forms to get refunds. If you filed, the IRS is probably just verifying your identity. When you respond to the IRS you’ll need your last 2 years of income documents and all the supporting information.
If you did not file, don’t panic. You’re probably thinking “How could this happen?” or “What else do they have?” or even “Could they have cleaned me out?” Chances are, yours was one of millions of identities compromised in a number of large scale breaches over the last few years. Verify your information with the IRS and let them know the return is fraudulent. You will have to file paper taxes this year. You may want to file an identity theft affidavit and engage a credit monitoring service. Check with your accountant and advisors.