This number called 4 times today. Answered it once without saying anything . There was silence then call disconnects

Exactly the same - silence then" goodbye"

This is a scam call.

silence, static, then goodbye!

Since moving to Victoria, and having no option but to use Telstra because they have monopoly in rural areas, I've had nothing but persistent nuisance calls, and I have an unlisted number. The do not call register is a joke because international callers are exempted from this. No amount of talking from Telstra will ever convince me that their call centre employees aren't responsible, or selling off phone numbers for profit to unscrupulous opportunists.

silence, then a polite (synthetic) "goodbye"