OMG! I was hacked by the same I.P address, too. I was in the verge of panic when I browsed the messages in my gmail account and saw that there was a change in my password and my account using a "yopmail account" or a temporary account. I was about to lock my account but I thought of an idea and luckily, I was able to recover my account.

How did I recover my account?
1. Check the new email address that was used in your hacked account. Since it is a temporary email, you can access it.
2. Log-in to your account using the "forgot password" setting. An email from the forum will be sent to the "hacker's temporary account." You can use it to access your account once more, change your password and add secret question and everything.
3. Once you regain full access of your account, delete all the messages of the forum in the hacker's account so he cannot "lock your account or whatsoever.
Hope this helps.