Caller: said Telstra

"Hello Sir" - did not know my name-, said they were "Alex" from telstra, about internet service and wanted to know if was the main account holder. I asked them "what's my name?" and they said "hold on whilst I look it up". I told them to email me and hung up., then called back from mobile within minutes with my caller ID blocked - "optus advises that the number has been disconnected"