I don't answer calls that aren't in my phone list.

I keep getting Sydney numbers I don't recognise calling me (including this one) and they don't leave messages which is a very good indicator that they are trying to sell me solar panels or something.

they're trying to sell you sh*t, or change your energy provider.

Spam, don't answer.

Financial trading services - apparently I entered my email address somewhere (they wouldn't reveal where) requesting a call back (wouldn't they need my phone number for that???).

Told them I didn't know what they were talking about and they tried their hardest to convince me I was wrong. Asked them to remove my data from their system and they ended the call.