I called back number (03) 4214 2012 rang once then gets disconnected automatically.

Received 2 calls from this number in the space of an hour, they did not leave a message.
I also received another call from a similar number (03) 4212 8008 an hour before the other 2. A bit suss

Keeps ringing constantly

spam - called twice - very long delay - from "compare your bill"

Caller: Energy

Trying to sell energy, became pushy and threatening and stated he knew where we live..

probably scam. They said about great offers etc

Electricity spam wanting to know who you were with , what discount etc

It ended the call when I picked up the call

They hang up as soon as you pick up.