The internet is certainly wonderful.  After all, it's part of our interaction right now.  And it's also the wild west, worldwide edition.
The wild west is the part that worries me.  People sometimes use the anonymity of internet postings and videos to be the adult versions of childhood bullies.  Some say the most astonishingly mean things to people they don't know.  While many people are able to just blow off mean comments, some of us are more vulnerable to these attacks.
People who have been victims of abuse as children or adults are more likely to take those posts of random verbal violence to heart.  The negative words worm their wicked way into already-bruised hearts and refresh the bruises, pushing self-esteem further into a little corner.
Kids and teens get bullied not only online but through their cell phones or iPads or iPods.  What used to be schoolyard face-to-face, I-know-who's-spreading-this-rumor bullying (I'm talking about you, Janelle Schroeder) has now retreated into the void of blocked numbers and anonymous texts or emails.
Bullying has become a focus of schools and families over the last few years with attempts at prevention.  Frankly, those efforts are not accomplishing much.  The human mean streak, adults and kids, is roaringly out of control.
So if you're being bullied - by strangers or known persons - you want to take some strong steps.  
First, don't take it to heart.  It's about the sender's own inadequacies and low self esteem.  It stings, but don't let it do you harm by taking it seriously.  Blow it off.  Practice not being a victim.  Be tough.
Second, talk about it. Get help.  Talk to a real friend, talk to a therapist, talk to a teacher or a pastor or someone you trust who will be supportive.
Third, do something.  If you have no idea who's doing this, block the incoming number or go to the length of changing your email or phone number. It's no "fun" to stalk someone who cuts you off.  
If you know who sent it and if it's threatening in any way, go to your county courthouse and apply for a harassment restraining order and report the contact to your local police.  Be tough.  Be strong.  Refuse to be a victim.