can you provide the specifics?
I think what you are saying is that you requested $4200 for the Recovery Rebate (line 30).
what did the IRS website say you received? If it states $2800, then do the trace suggested by @VolvoGirl
any chance you changed banking accounts since filing your 2020 tax return. Whatever you listed on the 2020 tax return (and possibly 2019 tax return, depending on the timing) is what the IRS would have used to provide the 3rd stimulus last March
