to have already written this off...

[Chippednailvarnish]

I've just been made redundant, so I am job hunting. Over the last few months I have applied for eight jobs, I've had interviews for four of them, but so far no luck and my confidence is slipping.

Last night I applied for a job online by email, it turns our the email address on the advert wasn't working. So I trawled through the internet and managed to find an alternative address and sent it to that one instead.
I then called the company this morning to check to see if they had received my application. To cut a long story short, they were really rude and basically put the phone down on me.
Then two hours later they email me and ask me for interview!

Am I being really stupid but I'm already writing this one off on gut feel alone?

You are presumably dealing with HR at the moment.
Unless you are an HR person it might turn out the people who interview you and who you would possibly be working with are quite normal and lovely.
I can think of several places I have worked where HR were gits but they were not representative

As someone whose husband works as a recruitment consultant and regularly has to deal with HR he is constantly ranting what a bunch of incompetent twats they are, how they go out of their way to make like difficult, interfering, slow at responding to anything, and finding ways to justify their existence etc. etc they are all the same - no matter what kind of company you work for.
It's just HR- not a a true reflection of the company. You don't have to work with the people in HR unless you are applying for job in HR in which case apologies :-)