A lack of proactivity? Contact Optus on LIVECHAT and they have people that will step you through the diagnostics and determine whether the NBN is working properly or not and if the issue is your home setup or something in the line.
Chat with the activation team everyday since 01/04/2019 and still not activated. Tested the Optus NBN modem and all good. Brought up the web browser and error displaying ‘no internet service’.
So its defintely an activation issue? Optus aren't saying that the line is all good from their end?
If that's the case then either its an Optus internal fix or Optus need to contact the NBNCo and hammer them to sort it. IME Optus are not very transparent when it comes to dealing with issue relating to the NBN. They also often don't seem to follow anything up unless you keep contacting them (i.e. they'll submit a request for action and then consider the task done).
All you can do is what you have been doing - contact them and demand they sort it with NBNCo.