what specifically is different? if it's unemployment ($10,200), there is nothing to do ; the IRS said it would figure out how much everyone is due and make additional refunds.
I filed my taxes in Early February before the American Rescue Plan Act was passed and I was billed for $330 because I received unemployment and did not withhold federal taxes from it. There is no way that I would owe for any other reason, as I made only about $19,000 in 2020 without the $6,500 of unemployment I received! I got a bill in the mail the other day for said $330! What do I do with this bill? And do I file an amended return, or do I just wait for the IRS to automatically correct my 2020 federal return for the ARPA changes?
Ok STOP ... do not worry or panic as this is normal this year. What happened is your Original return has been processed and the computer auto generated the bill since you did not pay it. Now your return is sent to the department which is handling the unemployment correction and if you will now be getting a refund then you can ignore the notice since it will not be valid once they finally make the correction. Do NOT muddy the waters further by amending the return as the IRS specifically said they don't want it.
As for the notice ... you can try to call the number and explain the situation OR just ignore it. The corrections are taking longer than expected so don't be surprised if you get another bill you don't need to pay before you finally get the refund.