It appears Optus don't have a very good tracking system . The "warehouse" seems to be its own department and what end when things are shipped to and from it is not something most staff have direct access to (many just phone across to ask someone to look into things). Some staff are prone to just making answers up (knowing they won't be dealing with you again). In general you won't be called back (assume that however you leave a call is the last you will hear of things so try get answers then and there)
At this stage I'd suggest you just make this a formal complaint.
You can try
and hope you get a responce.
I'd also write one though as these are possibly treated more seriously. Try keep the complaint brief. Leave out all the fluffy stuff and just summarise what's happened and what you need to fix the situation.
Ultimately you want to get an official complaint number. Unfortunately Optus departments appear to work independently so while your complaint is being handled its possible you'll be hit with late fees etc.
If you can't get an answer (and it is up to Optus to provide proof that the phone arrived at your home and was signed for by you) then forward the complaint on to the TIO (with the number) and they should sort it out for you. I'd suggest you don't waste much more time trying to sort it out yourself. Write the letter and after that the process should begin to work for you. The TIO works on your side and is able to direct Telcos how to resolve issues.