Caller: Scammer pretending to be telstra

Scammer pretending to be from Telstra got hung up on when I challenged them

I answered the phone and there was a few seconds delay before they answered (always a sign that it is probably a scammer) so I hung up. One hour later I got a call from (02) 8552 5392. Again there was a few seconds delay so I hung up.

Scam caller. Called back on private and it's an automated message saying they're web designers.

Unknown caller, no message left.
Checked number on google and it comes up under foreign website, so I suggest it's spam.