Rang and did not leave a message

Caller: Call center re: "Electricity Account"

Sounded like a scam, as we don't have a plan that requires any updates like this.
Definitely a call center, as the pause between answering the call, and the caller taking was delayed.

Insurance company

Persistent but no-one responds when call is answered.

Caller: Anna from Offer Assurance

“Anna” from “Offer Assurance” has a very thick Indian Accent.
I am assuming it is a scam of some sort

I called back number (03) 9088 1162 spoke to a guy who said I've reached Offer Assurance.

charity

They call and will not say who they are from. When you ask they hang up. Rang twice today about an hour between each call. You can tell its a customer centre as there is a pause when you first answer.