what to do when the ex fiance is witholding my childs ssc info?

we have lived together my childs whole life (3 years). now we are splitting, and for the last 3 years she has claimed my daughter on her taxes. well this year i wanted to do it, and when i looked intoi it, apparently i actually have the right to claim her, based of my adjusted income.

So when i tried to claim my daughter, it asked for her ssc, i asked my ex, she refused to provide, and has taken all paperwork out of the house to another location. I AM ON THE BIRTH CERT, i am a full dad, no custody agreement in place as of now, and i cant go to the social sec office due to the pandemic.

 

is it better for me to give up on claiming my daughter and come back next year better prepared?

or is it even legal for her to withhold such information?

 

Please help..