I don't think we know why the IRS is sending those EIC letters. It may be you don't qualify based on 2021 income but can use the 2019 lookback provision. Did you enter your 2019 income when you filed 2021?
You can look back and use your 2019 income for the EIC credit instead of 2020 & 2021. How to use the Lookback provision
https://ttlc.intuit.com/community/earned-income-credit/help/how-do-i-use-the-lookback-provision-to-m...
