Don't know who you spoke with at the IRS but they gave you incorrect information.
The Recovery Rebate Credit is based on your 2020 AGI, not 2019.
The IRS Recovery Rebate Credit Worksheet specifically uses the 2020 AGI from the 2020 Form 1040 Line 11.
Go to this IRS Form 1040 (2020) Instructions on page 59 for the Recovery Rebate Credit worksheet line 11 on the worksheet - https://www.irs.gov/pub/irs-pdf/i1040gi.pdf#page=59
