Rang on landline (where reported as '0 Anonymous') long enough to be diverted to my mobile (where reported as (02) 6111 2001) but rang off without leaving a message. Calling back produced a message that the number had been disconnected.

Again, rang off off after ringing for quite a while but left no message

Did so again. This time, I rang back and got an engaged signal. Robocalling?

Rang off, after quite a while, without leaving a message