Please contact the IRS immediately. Don't want to frighten you, but a duplicate SSN message may indicate someone has stolen your identity and has already filed a tax return under your name. Unfortunately, this is a common occurrence these days with all the identity theft going on. More info here:
https://www.irs.gov/newsroom/taxpayer-guide-to-identity-theft#:~:text=Tax%2Drelated%20identity%20the...
Good luck and I hope the issue is something less serious.
