facetime call goes to somone else! please help!!

my iphone 4 is hacked and when my girlfriend calls me in facetime someone else answer, and then the person that hacked my phone took her number and called her att Viber! what should i do?

it can be my cousin because we had same apple ID but 2 months ago i created a new apple ID just for me!

Does it help if I reset my iphone?