I have tried several times to follow the IRS instructions and can't get past them asking my email address.
IRS website for a the 5071C notice you received - https://www.irs.gov/individuals/understanding-your-5071c-notice
IRS Identity and Tax Return Verification Service website - https://www.irs.gov/identity-theft-fraud-scams/identity-and-tax-return-verification-service
If you truly not able to follow the website instructions, you can make an appointment with an IRS office to get verified in person.
https://www.thecountyoffice.com/irs-office/?bingcust=abdtco&msclkid=bd02403dd03e17d41f6c2610bda03cda&utm_source=bing&utm_medium=cpc&utm_campaign=ABD%20-%20IRS%20-%20PC%20240409&utm_term=the%20closest%20irs%20office&utm_content=Irs%20Office#google_vignette