Read the entire IRS notice carefully and follow the instructions in the notice for what to do if you disagree with it. Be sure to respond by the deadline in the notice. You might be able to reach someone at the IRS by calling the contact number in the notice rather than the general number.
If you purchased Audit Defense for your 2021 tax return, call TaxAudit at 877-829-9695, or report your IRS letter on the TaxAudit.com web site. Do not contact the IRS until you have spoken to TaxAudit. They might contact the IRS on your behalf.
If you did not purchase Audit Defense, you can get help with your IRS letter from TurboTax by calling 800-624-9066. See the following FAQ.
TurboTax Audit Support
Also see the following link on the IRS web site for more information.
Understanding your CP11 Notice
