Pathetic customer service

I am so angry while writing this post. I received a pair of Adidas, Mens adidas Response Boost Techfit Running Shoe (Size: 7) for my birthday gift. I was so excited as I always wanted this pair of running shoes as I run alot and believe strongly in the Brand Adidas. I tried it on and ow and behold it was one size too small. I normally take a size 7 I guess this brand is a small make. I thought ok I will take it back to the store when it was bought as I was told where it was bought. I got to the store spike to a sales person and explained that I do not want the money back I would just like a bigger size. The more I told the sales person I don't have a slip as it was a gift the more they told me I need a slip. By this time I was fuming and thought wow how and what poor customer services is this I mean what do I so with a small shoe. All I wanted was a bigger size the shoes are in a brand new condition and has not been worn. I mean like wow how do treat customers like they *******. I am so disgusted by this level of service from such a premium brand store. I want this sorted out and I will not leave it like this.