Caller: Woman purporting to be from NBN

Phone call from (08) 7092 2599. Sounded like it came from a call centre with many people also making phone calls. The woman who rang me unsolicited says they are from the National Broadband Network (NBN). Says my internet is slow and "can fix it". She asks whether my internet is slow. I reply "no comment". She then repeats that she is is from the NBN. I repeatedly ask how she is going to fix my internet. She then mumbles something I cannot hear. I ask again. The mobile call is disconnected from the caller's end.