The 600 was for the 2nd round Stimulus payment. You should have claimed it on your 2020 tax return. Check 1040 line 30 for it. What's on line 30?
The 1,400 is the new 3rd one. It is not combined with the first 2. It comes separately and is not part of your tax return.
So how much refund were you supposed to get on 1040 line 35a? Did they send you less? Do not include the 1400.
