Can I claim the stimulus credit if it was already given to the other parent?

Hello! My ex and I are supposed to alternate years when claiming our son on our taxes, so he claimed our son on his 2019 taxes, and got the $2000 credit. But afterwards, I learned about the 'loophole' that says he can only claim our son if he has paid all of the child support. Since he's way behind on child support, I amended my return to claim our son as my dependent. I filed my amendment in May 2020, just before the stimulus payments came out. It wasn't done processing until July 2020, and I got the $2000 in July when it was approved. But, in the meantime, my ex received the $500 stimulus for our son in May. Now, I received the 2nd payment yesterday, for only $600, I didn't receive the payment for my son. I assume it went to my ex, again. I don't understand why, because it was amended 6 months ago. My question is, can I try to claim the stimulus credit when filing my 2020 taxes so I can get the $1100 ( $500 + $600 ) that I was initially supposed to receive? I'm sure he was already given that stimulus money, and I don't want to get in trouble with the IRS if I claim it.