We had an issue with a blind we ordered to fit a window in our lounge, when it came it was the wrong size, they claimed it was my fault but I was able to prove it was their fault, however the owner refused to give us a refund. I found a form letter on the Consumer Affairs website and was able to fill in the relevant information and then send it off to the shop owner, a cheque arrived in the mail 2 days later fully refunding the amount we had paid him. The letter basically outlined our rights and said that if we didn't receive a full refund we would take the matter to the Dept of fair Trading. Might be good for you to put it all in writing, manager or owner etc might get it sooner and saves you having to go into the shop every week trying to catch up with someone who can help you.
If the top you brought was faulty then they have to refund you. very frustrating!
I can't remember exactly where the letter was but if you look at Dept of Fair Trading or consumer affairs online you should be able to find it.
wannawannabe - I have brought several tops at the same time without trying them on before, particularly if I have the kids with me or am in a hurry. Sometimes I'll try one on and then buy 2 or 3 of the same style in a different colour - could easily then get home and find one had a fault and need to go back and change it.