Tried calling my mobile. I didn't recognise the number so I didn't answer. They didn't leave a message. From the comments above, I'll assume it's a telemarketer.

Rang all day long about changing power company's, even after I said no the first time still called another 5 times to see if I'd changed my mind yet.

Some call centre for power company sales I think - keep ringing but never leave a message - called them back - Indian outcall centre

I rang back the number (03) 5317 8601 once but got disconnected