If you are experiencing difficulties with the IRS, know your rights as a taxpayer. Read the Taxpayer Bill of Rights (https://www.irs.gov/pub/irs-pdf/p1.pdf). Also consider contacting the National Taxpayer Advocate service (https://taxpayeradvocate.irs.gov/contact-us). And you may want to engage a tax professional who can represent you in this matter.
The IRS action of fixing tax liability that sets in motion collection procedures, such as charging interest, imposing penalties, and, if necessary, seizing property.