I e-Filed a 2021 Federal Extension today and it was rejected

Federal Extension
Rejected
Apr 15, 2022
Details for your rejected filing.

Error message: Taxpayer TIN in the Return Header must not be the same as a TIN of a previously accepted electronic return for the return type and tax period indicated in the tax return
Solution: This return was rejected by the IRS because the taxpayer's identification number assigned to this return has already been filed and accepted by the IRS. Please verify that you have accurately entered the taxpayer's SSN or TIN and make corrections if required. If no errors have been made in the entry of the taxpayer's SSN or EIN, it may be necessary to contact the IRS at 1-800-829-1040 for further guidance.
Code: R0000-902-01

We have verified the taxpayer's name and SSN are accurately entered.

The taxpayer called the 1-800-829-1040 number and I called PPS at 866-860-4259. Both of us got a message "Due to extremely high call volume, we are unable to handle your call at this time. Please try your call again later or on our next business day."

Is the IRS not answering the phone today due to Emancipation Day holiday today? What options do we have to file a federal extension other than waiting until the next business day Monday, April 18, 2022 to try to call again?