Sons Social Security Card

I think my son's dad is using his social security card to work to avoid child support they have the same name different birthdays and hes working in wyoming.how did his measly50 a month for two kids disappear to, yet hes working at the restauraunt.He fled to Wyoming and took my son across he states line,and I eVENTUALLY got him back however he has a domestic violence record and drugs and his whole family is vicious