You should get a form letter from the IRS that explains what the offset amount was for.
You can also contact https://www.irs.gov/taxtopics/tc203#:~:text=Not%20all%20debts%20are%20subject,for%20TTY%2FTDD%20help).
Disclaimer: Not a tax professional. Information gathered from internet links. Anything dated in June 2019 was posted in prior years and is before the 2019 limits and changes.
