I called back number (03) 8373 4758 it says the number I have dialed is not in service anymore.

Called me on Fri 19 at 6:30 pm. I heard some minor background noise, and then they hung up. I have been called from the same number on 18 Feb, and 28 Jan 2016.

Received a couple of calls from this number. Seems like a telemarketer

Tried ringing the number back and it keeps giving the message that that person is on the phone.

same Adelaide. sa

All I got when I answered the call was 'Good bye"

I also called back, they said that the number is not in service anymore.

Same here - missed call, but recorded voice saying it's not in service.... NOT a Telstra message though