Who called from 7812511014

Keep getting calls but they leave no message. When I actually answer there is no one on the other line. What is the purpose of these types of calls?  Does anyone know?

They have called me 5 times today even though I have the number blocked.  Before I blocked it, they would never leave a message.  These calls are so aggravating.

It doesn't even matter anymore if you're on the do not call registry. They are back-logged for years. I dont think they'll ever catch up

Don't think it will make a difference but all it says on the caller ID is SECURITY.

received several calls from this number daily. I finally answered and it sounded very noisy in back ground. immediately I said I was not interested and the man on the other end said "F*** You" then hung up. I have tried blocking this number but they keep calling.