This number is connected to an online porn site. I won't post the link so as not to spam but if you google the number you'll get a response for a specific young "lady" on the site. Of course, there's so much number spoofing that there's no way to know for sure who is calling. If you've been threatened, report it to your local police force. Don't respond, don't call the number back and block it if possible. If you're using a land line, consider getting a call blocker. Here's an 800 notes discussion forum on different brands:
http://800notes.com/forum/ta-ae7fb1decae9014/ ... -any-do-you-use
If you're using a cell phone, download a call blocking app. Many are free. Be sure you get one that allows you to block access to VM as well. Take care.