Caller: Credit card sevice

Scammers robo called regarding an Amazon suspicious $400 transaction on my credit card. When I was transferred to an male operator who spoke with a foreign accent, asked whether I did any transactions this morning. After saying no, he said there obviously was, and I said can you identify any of my credit card details he refused, and hung up.....This number was traced to a disconnected number in Callala Beach (south coast nsw). How do they obtain disconnected telstra numbers from which they use for their scams. TELSTRA DO SOMETHING ABOUT THIS ACTIVITY! This has happened so many times to us before...