Deductions & credits

My question is not referenced in any FAQ. In 2019 I filed single and signed a form 8332 for my ex husband to take the deduction for our children, that I have sole custody of. In 2018, I filed Head of Household with my children as my dependants.
I need to find out if I can get the stimulus for my children as well? Who should I call? It says the Guardian will receive the payment for the children, but since I did not claim them in my already filed 2019 tax return, how will they know that I am their guardian??
*My ex husband will not receive a stimulus payment at all, so I can't just have him forward their payments to me.