Per the IRS Website's IRS Operations During COVID-19: Mission-critical functions continue:
Taxpayer Protection Program: If you received correspondence from the IRS asking if you filed a suspicious tax return, you may use the online Identity Verification Service to validate your identity. Because the IRS cannot take calls or appointments right now, this is the only present option and is only for taxpayers who receive IRS letters asking them to authenticate their identity via online, telephone or in-person and confirm whether they filed the tax return in question.
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I tried to use the online Identity verification, but it does not accept my information which I know is accurate and says I must call, but they are not taking calls. This is in reference to my 2018 tax return, and now they will not accept my 2019 tax return.