Please read this topic, and follow all of the advice there:
Online blackmail. Read this first. viewtopic.php?f=20&t=580Please read that entire topic. Here are the main points in it:
DO NOT PAY THEM! They will only be back for more money over and over until you stop.
Block them in FB, change your FB username and picture. Increase your privacy settings in FB. Block them in Skype. Put Google Alerts on your name, and report any videos to the host of the website to close them. Do not answer any unknown emails, delete them without opening them, and do not accept any new friend on skype or FB.
The last post in that topic should answer your question.