How can you fix i phone if erased through i cloud account without password?

How can you reactivated phone that was erased by someone who changed password to I cloud account and then erased my phone, please help?? Went to best buy and they said can not be fixed without the new password changed by person. Of course not happening due to done out of spite! Any one know how to help?

There is no way to fix this without the password. How on earth did someone get access to your AppleID?