I call back. It said its mail box is full call later.

I called back number 0438 948 512 rang 5 times then goes to busy tone.

invited me to attend an important presentation WTF???

I tried to call back and I'm getting the message stating that "Optus advises that this number has been disconnected".
Obviously some kind of monkey business is behind this number.

not sure who but they left no voice mail message.