Just wondering if you can give me advice on trying to appeal the notice of final demand and having to pay $3300

Our mailbox is open and we didn't receive the reminder notice in time. Its an open mailbox and the letter was handed into us past the date.
I just went to nominate and it's saying we cant now!?!?!
Do you think this is sufficient to try and get the demand noticed dropped?
We are a hospitality business and are suffering enough to try and keep staff and definitely don't have the funds to pay this fine!
Any help you can give me on how to tackle this would be greatly appreciated.
Am Stressed out and freaking!