Called back and automatic message was "The number you have called is not connected". No message was left on my phone. I assume it was some scumbag telemarketer

I called back number (02) 5550 8656 rang 3 times then goes to busy tone.

Missed called from this number, no voicemail message was left so I assume it’s a scammer/telemarketer

The voice said after a few seconds "Good Bye". If they ring again I am blocking

I called the number back. the automatic message was "The call could not be connected, please check your number and try again."