Do you have 5600 on 1040 line 30 for the Recovery Rebate Credit? 5600 is the 3rd Stimulus payment for 4 people (1400x4). Line 30 is only if you didn't get the full amount or qualify for more. The IRS records show they already sent it to you.
Double check your bank statements and Check your IRS account (both accounts if married)
Your Online Account | Internal Revenue Service
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...
