This is obviously from a scam operator and this number (when called) is advised by optus as a disconnected number

Caller: Could be SmartUser

I rang back one time. American female voice: "Press (Pal?) t leave a message or press Star to call the operator " I didn't do either. If they don't identify themselves I regard it as a scam.

If it is a solar panel marketer it's probably Smart User that is promoting free eco LED lights, electric hot water services and solar panels. Their accents are difficult to decipher.. Different people from their set up keep calling, asking for an electricity bill, but if these anonymous missed calls are from them they never leave a message..

Caller: Solar Marketing

Trying to flog solar power