1200 was probably for the 2nd Stimulus check. The IRS has been adjusting returns that claimed it but the IRS already sent it. Did you get it after you filed?
A common adjustment is if you claimed the Recovery rebate credit on 1040 line 30 when you already got the Stimulus payment or got the second one after you filed or reported the wrong amounts or entered the wrong amounts in the 2 boxes. If you entered the total you got for both rounds in the same box it would think you didn't get the other one.
