After months of dead ends I've finally had confirmation from NBN (via Telstra) that my Fixed Wireless tower is indeed congested at peaks times. This issue has apparently been known about for well over 12 months and, up until now, no upgrade has been scheduled. NBN hope to have the issue resolved at some stage during Q3 to Q4 of 2017.
It boggles the mind as to how much money has been wasted on getting to the root cause of this issue. From wasted engineer visits, NBN equipment replacement (WNTD and ODU), additional routers and credits applied to my account. All of which could have been avoided if NBN would just provide information on tower and cell utilisation.
NBN have stonewalled us at every turn making the complete process an utter nightmare. No matter the troubleshooting you do (I resorted to trying another ISP on a spare UNI-D port) they'll ensure they do anything and everything in their power to try and turn the problem back to the RSP or the end-user.