I called back number 0451 274 784 reached voice mail but did not say for what company.

"Aaron" called, claiming he was an electricity provider and wanted to discuss our power bill. He wanted to set up a meeting with the business owner. I hung up on him and he called my colleague and told him that we were in fact the business owners (we aren't).

silent call

Called back and automatically went to voicemail with the recording stating the mobile number with the international area code for Australia. Me thinks it a scammer ... called after 8pm.

Silent call. Calls you and then says nothing. When you call back it says unavailable.

Rings + nothing...
Some idiots have a low threshold for entertaining themselves.