Have I been Daft...?

Help, I think that I have messed up, and am now not sure what to do.

I purchased a flat packed piece of furniture from a mail order company. When I built it, the doors wouldn't close properly. I contacted the company and although they offered to have the item replaced, I refused. I tried to fix the doors on the item, but that hasn't worked. I'm also upset because they say that the item is "wooden construction" but it is not wood - it is made from MDF. I want a refund or a completely different item, but the company are now telling me that I have accepted the goods, and they are unable to help me further.

What are my rights??

Thanks

Hi Tony, thanks for your input. While I am pleased at your reply, I am surprised that the fact that I was offered a replacement (which I refused) would stand against me. However I called the company, and they took some advice and have given me a refund on the item. Good news all round!