Ok ... the IRS sent the original stimulus probably based off your 2019 return and then sent more later based off the 2020 return once you filed it ... so check your bank account ... did you ever get a "PLUS UP" payment between May & December ?
As to the current issue ... pay up asap. Then if you did not get the + up payment you can have the IRS trace the payment ...
If you claimed a missing stimulus payment on your return but the IRS took it off you have to ask the IRS. They think they already sent it to you. Maybe it went to an account you don't remember. Or you got a check or a card. It was probably easy to miss the debit card in the mail and think it was junk mail. They have to put a trace on it.
Double check your bank statements and Check your IRS account to see when and what they sent you (check both spouse's 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...Your Online Account | Internal Revenue Service
