You will need to change your posting key using the hive wallet. Your active key may also be compromised, depending on what you did when you gave out your information to another scammer.

EDIT: log into your account directly at https://wallet.hive.blog and click "Change Password." For PeakD, read here or here for instructions to change your keys. Write down the new passwords/keys and save them somewhere safe! Set a recovery account while you're at it. Choose someone you know in person if at all possible.