ex husband keeping stimulus check from me and kids

What do I do? We are going through a divorce. He has left me and our two kids with nothing. Only 472 a month of child support. He has kept the full tax return of 10 grand. He is now keeping the stimulus check even tho i live alone with our two kids. I have nothing literally. I’m not sure what to do. I have nothing. I can’t even afford diapers. He doesn’t care. He has control

Issues and is mad I don’t want to get back together. Mediation is May 14 and It May be pushed back again.. in dire need of help.