Caller: Free energy saving devices scam calls

This number (03) 7031 9711) and (03) 7031 9712 have tried to call me a few times, and never left a message, except for once, which was silent except for background noise, which sounded like a call centre with multiple people. Thankfully I now have an app which blocks them, and for most that aren't blocked, I prefer to check each number manually, so I don't get false negatives, and miss calls that are genuine. Now that I know, their numbers have been blocked.
They are most likely the idiots trying to offload their supposedly free energy saving devices. I have been getting so many calls from these scammers, that I have a new tactic, which I hope will work. I'll answer the call, and when they make the appointment, I'll agree to it, but sound like I'm not sure what, or who they are, then when they come to install their wares, I answer the door, and tell them that we have no idea what they are here for, and that I'm not interested. Hopefully with enough visits, they will get the message.

Probably survey or polling re referendum

Missed call. Called them back but getting engaged tone.