I missed a call from this number

Also got a call from this number today. All I could hear was something about pressing a number to opt out.

I have just received a call from (08) 7135 0591 and when answering, the person kept quiet for a while. And then immediately laughed a bit and said " Sorry Sir, I just couldn't hear you there for a bit, I will call you just now", and hung up.I tried to follow back the number by calling it back, but all I get is an answering machine. Please help us identify this number.

Who are these people..?

These are the guys who are wanting to scam us for airtime saying that we won a prize of R145000.00. When you call back you are supposed to buy plus minus R90 randw worth of airtime and sms the pin numbers to them befure you supposedly can lay claim to your prize money.  If i get a hold of these guys who knows what is going to happen