I missed the call, called back, got a message saying "please hold while I try to connect you" in an American accent. Naturally I hung up. Smacks of a scam, confirmed by other comments on this site.

Missed call, but call couldn't be returned as number is not connected.

Scammers using a series of disconnected numbers registered to serial telecommunications act breachers Chime Communications Pty Ltd as a fake caller ID to continually harass people even though they are on the do not call register.