Someone Hacked My Account And He Used My Messenger To Chat Some Harrasment

First, dont be worried about that. Relax yourself and there exist a solution for the same. The below steps will help you.

If your facebook account was hacked by someone and you really want it back this tutorial would help you get it back.

Step 1:
First goto this link. https://www.facebook.com/hacked
Click the button "Your account has been Compromised".

Then type in your email address, Login name , Full Name or your specified Phone No.

Then facebook would search for matching users. If you still don't see your account, try entering something else other than the one you entered.

( for example if you entered your phone number and it didn't work try entering your email or Login name.) Most of the time using your email would be the wisest choice.)

And hit Search. :)

Step 2:
Well now the kind of difficult part begins. But I don't think it would be for you.

Now for this step you got to enter your account's password. Well if you knew the password you won't be here anyway, cause you don't know your new password the Hacker's changed, enter your old password. The password that you use, to enter into your account before you got HACKED

Step 3:
Then cause you entered an old actually now wrong password this page will come up.
Well no need to be down yet. Just click the reset my password button.

Step 4:
Your primary email would be changed so well of course you don't want to send your reset your password link to the hacker's account so, Click "no longer have access to these?" link.

Step 5:
Well now you almost got your account back.
Now write your new email address that you want to send the change password link as well set as your primary email.

Step 6:
Well now, follow the next steps and you would have your account back in 24 hours.

Hope this helps!