Threatening calls saying from Australian Police

[Suziq66]

My elderly  parent has received threats of arrest coming in on calls between 3am and 4am purporting to be Australian Police , 3 mornings in a row but we cant find trace of a number on the landline. How can I stop these calls.

It is not a person but a recording that is played saying if she puts the phone down she will be arrested and charged.

We have told her its a scam but it is very worrying to an 85 year old. How do I help, any suggestions?

[caesarome]

Do they have the Sky Talk Shield enabled on their line as it might be possible to block these calls via it:

https://www.sky.com/help/articles/dealing-with-nuisance-phone-calls-and-texts

Can they be blocked by their landline phone itself as again it might be possible to do this.