Caller: Dean

I had some issues with my internet speed and launch a complain with Telstra through app in the morning. After around 4 hours, I received a call from this number that it is from Telstra and mu IP is in public domain (at a huge risk) and this person wants to work with me to bring this back to private. The accent was Indian and background noises bit chaotic. I said, I don't want to give any information unless call is from Telstra numbers and asked the number to call him. He provided me Telstra number 13 22 00 and hastily dropped the call. When I called Telstra, they informed that no call has been made to me from Telstra and this is a potential scam.
I am unbale to connect the dots that how these scammers are becoming so powerful and how this person knew that I have any issue in internet and have launched a complain with Telstra. Is Telstra system hacked or scammer are sitting in my mobile?