This is just my opinion, no rudeness intended,
Why ruin your chances of passing stage 3 by simply not turning up? If I was the HR representative in charge of your day on Tuesday I would scrap your application despite however many emails you send. The least you can do is turn up anyway.
With so many others failing at stage 1 and stage 2 and in both cases probably losing out financially in the process, it seems quite unforgivable for you to simply not attend your stage 3.
