Calling back private numbers?

I have been receiving calls from blocked numbers to my cell phone, they have been calling me up and abusing me over the phone, and i would rather find out who they are then get a new sim card. So i was wondering if there was a chance i could call them back or trace their numbers? I have a telstra iphone, if that makes any difference.

How did Telstra answer your questions?

Id ring up telstra on 125111

You can contact the police and ask for their advice. You can also ring crimestoppers on 1800 333 000 or http://www.crimestoppers.com.au/
From telstra site
Nuisance and prank calls can be a serious annoyance if they continue over a long period. We know that these calls can sometimes be quite distressing, so we've set up a dedicated Unwelcome Calls team to help you stop the calls in these situations.
You can request a callback from our Unwelcome Calls team by completing our online form, or by calling 13 2200 and saying "unwelcome calls".
http://exchange.telstra.com.au/2012/07/10/how-to-stop-unwelcome-and-nuisance-phone-calls/

YOU said that you are receiving calls from blocked numbers to your cell phone. But the blocking depends on your telecommunication service provider. You should better contact your telecommunication support centre.