75% of the issue here is not whether your kids are listed as dependents. Mine are listed as dependents, technically, as well. The main area to check on your tax return is page 1, in the Dependents section, to see of the Child Tax Credit box is checked off. If it is NOT checked off, then this is probably the reason you didn't get the extra $500. And even further bet that the Other dependents box is checked off instead.
I'm sure there could be other reasons you didn't receive the $500 but I believe this covers a large majority of the reasons.
