IRD Penalties

Long story short,

I am a self employed contractor sole trading under my name so my personal IRD number. However, I created a business early this year at the end of April with the intention of trading under that business once I was better established, I haven't traded under the business name at all this whole year. For the sake of keeping this short, I had to switch to trade under my personal IRD as a sole trader in order for me to get some money to be able to provide lunches and such (you know the story)

I came home today to find a letter from IRD for my business stating that I owe them $4,500.00 due to not filing a GST return even though there was no such warning that this penalty would be applied had I not filed a GST return or even a letter/email requesting for this information. There has been no trade or services done under the business name so the GST return would be NIL. I am scraping the barrel as it is so I have come here to ask for some advice on what to do next.

Yes I know, silly of me to not file the GST return but it slipped my mind while I have been trying to stay on top of other things.

Any help would be appreciated.