Nike mercurial soccer boot problem- poor response

I bought a pair of Nike mercurial soccer boots just a week ago. When I tried it on in the shop, I tried on the size 7 on the demo and it fit perfect and comfortable. The sales person did not really assist me. I then purchased a pair of size 7 boots. I carried them for my first pre season friendly game on the weekend and when used, I noticed the right boot causing extreme pain and discomfort to my foot and this was unusual as the left foot was fine, furthermore, this is my 3rd pair of Nike mercurial soccer boot size 7 (so this is my regular shoe). After a few minutes into the game I had to stop and remove the shoe as it made my one foot sore. This did not happen with any of my previous two boots of same make,brand, and size. <br> I took the shoe back to gateway total sports and explained the management person the issue with this boot on the one leg and mentioned that this was not the case when I tried it on in the shop. He was not interested. He said that they cannot change it as its been used. I cannot use this shoe that I invested so much money on and I am disappointed that this shop cannot even help me. I don't feel that they deserve my support in the future due to this.<br> <br>