I have 79 blocked phone numbers - all belonging to Credit Corp or their mates. Surely that has to be illegal.

Caller: Scam, claiming to be Credit Corp

Saying I owe money to a Nigerian uncle I didn’t know yet because he lent money to my father when they were kids. I’m not even Nigerian

It's known as stalking, and that's definitely 'illegal'. But in my opinion, the whole legals system is 'illegal'. Look up definition of Licence in a law dictionary for a good clue.
Credit Corp. Treat with disdain.

I called back number (07) 5512 2486 spoke to a guy but did not say for what company.