What error message are you getting if any when you try and enter the chat? I have found that live chat link to be a bit hit and miss depending on what mobile device you are using. Having said that I just tried it on my Android phone and it seemed to work. Have you got the Optus app installed on your phone as this also has a live chat feature that might be worth a trying.
This is an issue for me for the last few months! Come on Optus.
Desktop computer, Windows 10 and Windows 8.1, On older and latest version of Chrome.
It works okay on the same computer with Firefox at this stage. The links don't bring up the pop up in Chrome, just does nothing.
Please look into Optus