I called back number (07) 5644 2800 reached IVR for a company called NBN CO a broadband network company.

Then why don't you leave a message? So we know that you aren't a scam call???
VERY ANNOYING!
Because I NEVER answer a call from a number I don't recognise, so you will NEVER get to speak with me

NBN National Broadband Australia calling to confirm with customers who are changing over from copper phone cables to optic fibre about their emergency Medical call systems and back to base home alarm systems. Legitimate number.

Call was from NBN Co. Legit Call

Yes its is NBNco ... Its the inbound call center.
If you are currently getting NBN installed or have applied for it then you should call them back. It may be important to your installation.
However if they contact you its more likely that you have contacted them or your internet provider and they are returning your inquiry.
Not scammers, the call center does not make "sales calls".
NBNco does not "sell" to the public, only to actual service providers like TPG for example.
You may have contacted them on a 1300 or 13 number .. however if they call you their actual number is displayed as caller id (07) 5644 2800 ...
How do I know ? I work there ;)

I am sure it is NBN Co

Called but didn't give me time to answer

I got a call from this number but the connection was really terrible and I couldn't understand anything they were saying. Would be so funny if it's actually NBN!

This is the National Broadband Network. They are not scammers as people have previous mentioned.

Nbnco

They keep ringing me everyday

Scammers or some sort of low lives.

SCAMMERS