Letter 6475 is only reporting the payments the IRS sent out. It would include the 1,400 they got for you. You don't have to report it because they got it. You won't get a letter.
If you were a dependent on a 2020 return but filing independent for 2021 you can get it now and they don't have to pay it back. So say NO you did not get one because you didn't one, your parents got it.
The 3rd Stimulus payment is really based on 2021. The IRS just sent the checks out using 2020 to get them out fast.
See IRS Topic B first question
Questions and Answers about the Third Economic Impact Payment — Topic B: Eligibility and Calculation...
