Deductions & credits

For 2018 I filed Married Joint with my then-husband. We had 3 dependents. In 2019 we had a baby and then were divorced. I have filed my 2019 taxes and was able to claim 3 of dependents as Head of Household. My ex-husband has still not filed his taxes for 2019. However, he received $3,900. I received nothing. I should have received $2,700 based on my 2019 taxes. Why did his 2018 ones trump my 2019 filing? I am guessing that since my newest baby wasn't on his 2018 taxes, that is why a total of $500 is missing. Should I still be expecting the $2,700 for my filing also? I guess sometimes getting taxes done on time is a disadvantage.