Have anyone had such a problem before?

[ravengily]

Have any have this problem before? If you have experienced before what did you do?

[Critter-3]

Did you click on the DETAILS button to find out what they changed ???   

Code 9021 is for a "math error" so did you have an amount on the form 1040 line 30 ?  If so what that same amount your total refund ?   If so the IRS disagrees with the credit on that line. 

If the IRS says the stimulus was sent but you did not get it then you will have to have a trace put on the missing payment:

https://www.irs.gov/newsroom/questions-and-answers-about-the-third-economic-impact-payment-topic-j-p...

[SweetieJean]

Also see

IRS is confusing taxpayers with math error notices: report (fastcompany.com)