Does the IRS website indicate that you were sent less than what was reported on your federal tax return Form 1040 Line 34? - https://www.irs.gov/refunds
If your refund is short $2,800 then that is because you said you did not receive the 3rd stimulus payment and the IRS has records that show you were sent the 3rd stimulus payment so they removed the $2,800 Recovery Rebate Credit that was entered on Form 1040 Line 30.
Go to this IRS website for your tax account to see if the 3rd stimulus payment is entered - https://www.irs.gov/payments/your-online-account
If you are Married Filing Jointly also check your spouse's tax account.
If you checked your bank account in the March - May 2021 timeframe and there is not a $2,800 EIP3 payment from the IRS then go to this IRS website for how to start a trace on the payment - https://www.irs.gov/newsroom/questions-and-answers-about-the-third-economic-impact-payment-topic-j-payment-issued-but-lost-stolen-destroyed-or-not-received
I just talked to the IRS on mine because I had $2800.00 exactly taken out and they said yes its that recovery rebate- They show it was issued in my bank acct.- If you call the IRS because you didn't receive it they will go thru your bank statement over the phone with exact dates to locate all of them were sent.