Caller: Just another scammer.

Do not ring them back. They rely on knowing the number is active by this action and will hound you ceaselessly from a variety of (02) 9000 numbers.
If you must ring back do it from a pay phone. Alot. They appear not to like this tactic.

No ID, deleted without answering. Will phone them on railway landline Telstra phone which is now free.

Caller: spammers

changing power companies...indian call centre

I don't answer calls I don't know

Rings constantly from different numbers, never leaves a message. All numbers start with 9000.
Blocked again.

No message left, called back - number disconnected

Spam - I turned off my phone ID and rang back within 1minute and received an optus message saying this number was disconnected