If you call the number back, it will tell you that you have received missed a call from CPA Australia who were calling to update your Student Passport account with CPA and advises you to visit their website to update your membership.

Got a call from this number yesterday and today, missed one and didn't answer the other. Not expecting any calls from Australia and no idea who it'd be - though my best guess is someone who grabbed my number from a domain registry.

Found this number on my caller id.

Unknown number, but I missed the call, and they didn't leave a message. Probably marketing I'm guessing.