i called back number (03) 5202 4105 spoke to a woman who said I've reached a switchboard but did not say for what company.

I would say Credit Corp

When called back, they refused to tell me the company name unless I identified myself in full, so definitely a debt collector.
Possibly Credit Corp as stated in previous comments.
When I called back, I was told there is a number of different companies in the office, but would not list them by name. She went on to explain that I needed to identify myself and then she would tell me the company name for the person who called me. In other words, a debt collection agency contracting their services out to multiple companies.

Caller: Credit Corp

Definitely blocked

Caller: CREDIT CORP c*ntS

CREDIT CORP c*ntS