Problem Solved. Went to their web-site and via the 'contact us' advised I would lodge an official complaint if these unwanted calls continued. A day (and two more calls) later, received this email:

Hi Ian.
Thank you for your email.
I apologise for any inconvenience caused.
We have removed your contact number from our automated dialler. You will not receive any further calls from Red Energy on 03 9435 xxxx.

Kind regards,
Jonathan McKibbin
Customer Solutions Consultant

T +131 806
F (03) 9425 0589
W www.redenergy.com.au

Like other comments, constant calls that just hang up. Rang this number back and got a recorded message, "Hi, you have been called by Red Energy...." at which stage I hung up. Caller identified! They are not my supplier and with these antics, never will be. Will now go to their web-site and see if I can leave a similar comment. Urge others to also do so.

I've had at least 3 calls from them.... afternoons while i'm at work...with message left on answerphone  just saying hello,.... hello.... hello..... and sometimes laughing.....but then no message to phone back.... and so I thought it may be a friend trying to get hold of me...but then I've had no answer when i called back in the evening. It rings and rings and then goes to what i thought is an engaged tone or it's been hung up (not sure).I've also recently got several obvious telemarketing messages on my answerphone too... but this sounded a bit different Could they have made it a premium number?... so that they make money from anyone who tries to phone back??.So i thought I'd do an internet search on it... and found this site.... which i hope is genuine.

number keeps ringing and hanging up

I too am getting calls from this number on my mobile.  I haven;t had the chabce to answer it yet as it only rings a couple of times and then they hang up.

Fred,Got a couple of calls from this number a few minutes ago - does anyone know if the telco/s can do something about these calls? I am on the Do Not Call Register - and if I do get to speak to the mysterious caller/s - I will tell them precisely where to shove it.

Fred,

Got a couple of calls from this number a few minutes ago - does anyone know if the telco/s can do something about these calls?
I am on the Do Not Call Register - and if I do get to speak to the mysterious caller/s - I will tell them precisely where to shove it.

No wonder. I couldn't hear clearly where they are from as it was a bit noisy at their side. Then he started to talk about electricity discount in Victoria and NSW.