I called back number (02) 9051 2523 it says the number I have dialed is not in service anymore.

I'm also getting these calls, they originate overseas and I get the same result, no company name & asks me to please hold on the line. My phone is not set to allow international dialing so I can't ring back.

This leads me to the big question "Am I getting billed for these calls?"

I called the number back and it just thanks for calling customer service, no company name and asks me to please hold on the line. So I hanged up.