No voicemail was left. Suspected scammers. As others have advised never ring them back as it just confirms your phone number to them. If they are genuine they’ll ring back or leave a message but even so who wants to get involved with someone doing unsolicited calls. Careful people.

Did not recognize number, did not answer, no message left. Rang back recorded message "Due to temporary service difficulties we are unable to connect you. Suspect a scam, blocked.

I called this number a got a message played -> "Due to temporary service difficulties we are unable to connect your call at this time. Please try again later. OIM1"

Caller: No message left

If you don’t recognize the number, DON’T call them back

Called me on weekend- did not leave a message

Scammers

Bitcoin

I called back number (03) 8594 2270 was put on hold music but no one answered the call.