Turbo Tax Said IRS Owed me an additional $1000 as per my bank statements, but IRS says otherwise?

Did you get the IRS 6475 letter yet telling you how much the IRS says they sent you ?   Those are still being mailed out.   Is it possible that they sent out some of the stimulus based on the 2019 return   and then sent more later once the 2020 return was processed or reprocessed once they took the unemployment or PTC adjustments into consideration? 

Sadly  if the IRS says the entire 1400 was sent but you disagree then you will need to have a trace put on the missing money ...   

https://www.irs.gov/newsroom/questions-and-answers-about-the-third-economic-impact-payment-topic-j-payment-issued-but-lost-stolen-destroyed-or-not-received

The 3rd stimulus payment should have been for $1400.   You told TurboTax that you only received $400, so you claimed the remainder of $1000 on your tax return.  Now, it turns out that the IRS says they already sent you the full amount of the stimulus payment, so they denied your claim for the $1000 credit.   

You can use this link to view your IRS account to see what payments have been made and applied to your account to:

Access Tax Records

• View key data from your most recently filed tax return, including your adjusted gross income, and access transcripts
• View information about your Economic Impact Payments (stimulus checks)
• View information about your advance Child Tax Credit payments
• View digital copies of certain notices from the IRS