The only refeerence you need is your PPSN. Ther are huge bcaklogs (average 6-8 weeks or more in many offices) so not hearing within 2 weeks means that they probably haven't had a chance to even look at your claim yet! whoever told you that was being optimistic, I think.
The 'on-line notification' is really just an email that is forwarded on to the local office relevant to your address, who then contact you to tell you to come in. It's a nonsense, in my opinion, there to fool people into thinking they are really 'applying' when they are not.
I think you have a very strong case to have your claim backdated. If you notified them on line, you are justified in thinking that they should act on it. If they didn't, it's not your fault. I'd imagine anyone worth their salt will see this and allow your claim from the date you notified them.