You each got a letter 6475 for 2800? So 5600 combined? Do you have 2 dependents? You didn't get the 5600? And you checked your bank accounts? They might have sent a check or debit card which would be easy to miss and think it was junk mail. The 3rd Stimulus payment came out starting in March 2021. How much was on your tax return line 30?
You don't need to amend for that. If the IRS thinks they sent it to you but you didn't get it request a trace for a missing third Stimulus payment
https://www.irs.gov/newsroom/questions-and-answers-about-the-third-economic-impact-payment-topic-j-p...
