Federal refund - Missing Form 4868 Extension Money

Hello Everyone, I did my FY2020 tax extension in April (to extend the deadline until Oct 2021) and during that time I paid $XXX as my extension amount along with Form 4868 to IRS.  In July when I did my taxes it appears to be I need to get amount $YYY ( My refund amount for FY2020) + $XXX (Extension Amount) = $ZZZ ( Total refund).

 

But after i filed my return in July, IRS refunded me only the amount $YYY and they forgot to refund me the $XXX i paid for extension.  I am supposed to get $ZZZ, but i only got back $YYY.  What is the process to get the difference money $XXX from IRS?