Non functional office chair

I am so unhappy and so disappointed in the way the cash converters handle their customers.I had bought an office chair on Tuesday and found that when I got home to use it the chair was very uncomfortable; had a crack underneath and also very unstable. I took it back on Saterday and they refused to refund me and they didn't have another chair in store. They told me that I should have brought it back within 24 hours and it doesn't have a guarantee. No where does it advise customers of this. I'm being told when I get there that this is the story. So please help me with this coz I don't want this chair at all!