answered call, silence for a few moments then beeped and automated voice said "goodbye"

Hung up when it went to voice mail. Called back immediately. Recorded message 'The number you have called is not available from this service'.

Same experience as you. I went to messagebank on returning home, no message just silence then beeped and automated voice said "goodbye". There must be a way to stop all of these sorts of calls, they are so annoying.

Caller: Unknown

A very argumentative sub-continental guy who claimed his name is "Mark" and was calling from the "Call blocking registration department". 5 minutes of amusement giving him the run around. Clearly a scam.