Like many of you, they rang twice and then immediately hung up. A robo-call tactic to get dupes to actually call them back so they can be scammed.
These "people" are parasites and need to be prosecuted to the full extent of the law to make them stop abusing the system. This is why I have to screen all of my calls and never answer any number I don't know, even if its from my own area code. Even if you block a number it does no good, because they detect the block and just call you on a different number. Its sad we live in a world where people without morals do this.
They are scammers that are fishing. They call and hang up to see if first the number is valid then if you answer or call they try to get information from you to get your identity or to just generally steal you credit info.