Rediffmail.com India — My rediffmail account has been hacked

I would like to report about a mail id - [protected]@guerrillamailblock.com which hacked my rediffmail account [protected]@rediffmail.com.
On the mail he/she has stolen all my personal datas and contacts. As mentioned my him/her that they have been succeeded doing so when i visited adult site. While searching for a movie or certain details on google their are multiple adult site and advertisement which mistakenly gets clicked, though i go back from the pages immediately. I don't even exactly remember from which site they got this access. Also have threatened me stating that to pay a certain amount otherwise would leak all my personal data to the linked contacts.
It is a serious crime and you should look into this matter as soon as possible and please suggest me important measures i should take to protect further.