Caller: Unidentified from 'Capital Centre'

Caller said they were from 'Capital Centre' and based in London, but showed a Sydney number. Calling back does not go through. Became very defensive when I tried to identify who they were and would not give a registration number (claimed they don't need one). They asked for personal information (which I did not give). Had several calls from the same 'Capital Centre' from different numbers, usually ends with the caller hanging up on me as they find I won't fall for their tricks.