Who called from 7702130811

This number keeps calling. They won't leave a voicemail.

These jerks call, then when you answer, the line goes dead.  When you call the number back, a male recording informs you all of their agents are busy.

This number keeps calling but doesn't leave a message.

They don't leave a message.  If you call back a man's voice says all agents are busy and they will call back within a day.  They ask you if you feel you have been called in error to press "1" to be removed from their list but as soon as you do so it disconnects you.  I would bet money this is some kind of collection agency trying to collect money you don't owe to a company you have never heard of.