I can’t tell if you are complaining because you didn’t get the credit on your 2020 tax return, or you are complaining because you have not received the advance payments for the 2021 return. If you are complaining about 2020, print a copy and make sure everything is correct, including form 8812.
If you are complaining about 2021, there is really nothing you can do. The IRS is so backlogged, it’s a minor miracle that anyone got an advance payment. The IRS may have a web site later this summer where you can modify your status. If not, you would get the full amount as part of your tax return.
