can i claim my son when i have custody

can my sister claim my son even though i have custody of my son .my cps case has been closed i'v a letter from cps stating that i have the rights that the case has been ruled out n that i can pick up my son anytime but my sister refuses to return my son n she's trying to claim my son as her dependent she claiming all son's benefits .Can i file a report n can i claim my son even though she refuses to return my son