I no longer answer calls to my landline if
Number Withheld or
Private is shown as caller ID. I have a Panasonic phone and have all our business, banking, doctors, dentist, friends and family phone numbers recorded in our phone and set with a different ring tone and default ring for all other calls.
We are on the
Do Not Call Register and recently one particular number kept calling from early in the am until late in the evening. It was an Australian phone number. I called Telstra and asked their advice. After giving dates and times they advised that this particular number could be permanently blocked but our dial tone would alter. It is now a long 'flat' sound.
Only helpful if you can capture the caller's phone number.
From Telstra
Australian telephone numbers used primarily for private and domestic purposes are eligible for registration on the Do Not Call Register. These include fixed (or landline) numbers, mobile phone numbers, satellite numbers and voice over internet protocol (VoIP) numbers.
Registration is free and will last for five years at which point the individual will need to re-register their number in order for it to stay listed on the Do Not Call Register.
And yes I still get unsolicited phone calls from charities and people offering free investment advice, selling solar panels etc etc as their Australian phone numbers are shown as caller ID with a default ring tone. I can choose whether or not to answer and if the call is unwelcome I always state this phone number does not accept calls such as yours and please remove our listing from your database and end the call.
Have an delightful elderly friend who is a bit of a character. He does not have a computer and the man from "Windows Technical Support Dept" had greatly difficulty instructing my friend how to turn on his computer.

He has been known to answer the unwelcome calls from 'overseas' with Police Constable Jones...and the caller usually hangs up

Cheers

Cando