Called at 3 am!  and then there was no one there!  F*****s

That's not always someone trying to scam you.(although at 3 am its difficult to see how it could be legit). Robocall systems and many telemarketing systems operate like that. They dial ten to twenty numbers simultaneously and then drop all responses except the first one. That usually guarantees they get a response on every ring. Also you have to be very careful about assuming these numbers are meaningful. Most of these numbers are voice over IP numbers, so you are actually getting a call from a server in a network which hides the real number and it injects a false number in at the last point in the call. It basically allows them to spoof a number and the telecom system will not be aware of it because they  called from a genuine number as the call was being routed through the network, and then when they have passed the last switch they spoof the number and it appears as any number they choose. At that point the telecom system no longer cares since it has successfully routed the call.