Yes, you are correct, the IRS will correct calculation errors only when the Recovery Rebate Credit has been already included in the return.
To contact the IRS, call 1-800-829-1040 and they are open Monday through Friday, 7 AM to 7 PM. For more contact resources, see IRS Let Us Help You.
For more information, see: March 1, 20201 Update for 2020 Recovery Rebate Credit — Topic G: Correcting issues after the 2020 ta...
