I called back number (02) 8199 2019 rang 3 times then goes to busy tone.

I received a few calls from this number in the last 5 days. A female asked me if it's a good time to talk as she urgently needs to speak to me. I didn't have time but asked what it is about. She didn't want to tell me without speaking to me in detail. Just hung up on her.
I called back some time later. After 5-6 rings a male picked up. I asked who they are. Without giving him my mobile number he didn't want to tell me anything. - So, I just blocked their number.

May be credit corp