My 2020 return was e-filed and accepted by the IRS. However, many months later the IRS now says they have no record of my return. What should I do?

Original 2020 1040 return e-filed via TurboTax on March 16th, 2021. Received a letter from IRS in June 2021 requesting additional info, which I supplied immediately. Phone call to IRS in November 2021, at which agent confirmed the return has been corrected as of September 7th, 2021, but still waiting for refund to be processed. Finally, called IRS again on February 7th 2022 to inquire status and was told "we have no record of a processed tax return" for 2020.