Are you Single? 2020 $1,800 sounds like the 1st & 2nd Stimulus Checks. The first 2 Stimulus checks were for 2020. The first one was 1200 (2400 married) and 500 for each dependent under 17. The 2nd one was 600 per person and dependent under 17. It came out in Dec 2020 - Feb 2021 but went on your 2020 tax return.
Check your 1040 line 30. The Recovery Rebate Credit on line 30 is only if you didn't get the full amount or qualify for more. The IRS shows they had already sent it to you and you tried to claim it again. Double check your bank accounts and check your IRS account (both if married) to see how much the IRS sent you.
https://www.irs.gov/payments/your-online-account
