Needed to vent

My daughters father’s family has always hated and now they convinced him not to give child support because she does not have his last name. She’s 4 years old and he has only given 800 her entire life. He’s a piece of shit now saying she’s probably not his. I shouldn’t be having to beg a father to help out his child. Its clear he does not care about her

Does anybody know how child support works? He’s illegal but I know where he works and lives. He isn’t on the birth certificate either since he lived in a different country.