It's actually a number for either a back to base alarm or any sort of home monitoring device such as a heart alarm or smart caller. It functions by making a call out regularly to confirm the device is working, and additionally whenever it is activate. Each time these calls are made it is the price of a 1300 call.

Telstra bill for my elderly mother was also the same

This number appeared on my grandmothers Telstra bill twice. one for 8 seconds the other for 7. She was charged 35 c per. Is this number Telstra uses when it decides someone is not paying enough on their bill?