Return not taken

I went to return sneakers I bought on the 16th of December at the Boardwalk Side step store. I wanted to return them at the Greenacres store but my return could not be processed because they say I damaged the shoes. I wore them once and got blisters so the reason for the return is an incorrect fit. Tell me how I damaged the shoes I wore on once and I am still within the 30 day return period? This is the first time I have bought an item at Side step and it is my last now I must sit with ill fitting sneakers? Can anyone please assist?