Can i get my money back? (clothing)

I purchased a dress 1 month ago, i tried to take it back to new look today because i found that there was a manufactor fault with the dress;
the stitching had come out and if you turned it inside out the stitching was still attached so it was as if the machine had just done one long stitch rather than lots of little ones.
They assistant told me it was 2 days out of the 28 day returns policy and that she couldn't do anything. Now i work in retail and know that the 28 day returns policy doesn't affect my statuary rights when returning faulty goods. I didn't have too much time to argue as i was on my lunch break but she basically wouldn't do anything for me.
I will be returning tomorrow to speak with their manager.

What i'm asking is am i entitled to a full refund? or does it have to be a repair or replacement?
i've worn the dress once and had it a month and the fault was obviously there when i purchased the item.
I'm also a bit annoyed that i now have to go back into town tomorrow as the assistant wouldn't do anything for me today.

thanks very much for your help!
the dress was only £20 - not like it's even an expensive one!
but thanks for the number too! I did ask her for a customer service number in the shop and she said they don't have one which i thought was odd.