Lack of customer service and transparency

I am a first time customer to their establishment,I bought a pair of Nike Airforce 1 sneakers from them on Friday. While in the shop i had no assistance the owner or manager was walking about but never offered to help.I accidentally took the wrong size,i was looking for a UK 6 and ended up with a size 4 ,however on the box it displays US 6. So i went back on Monday to ask just for a different size ,upon entering the store the Manager walked off and i was told by the staff member to read the sign.

I explained to him that this is my first time purchasing from them and i read the receipt stating you are allowed to bring back the item within 7 days and nobody assisted me in the store in order to explain that policy to me, at the till point the lady who assisted me also just took payment and never explained the returns process. I think that is really unfair to not have assisted or even informed me about the returns policy ,i tried to explain that i am a first time customer and i have never heard of such policy even on sale items ,i do acknowledge that different rules or policies apply but if i wasn’t informed by any member of staff how is that transparent. I was told to sell the shoe’s to someone to get my money back and i was actually willing to add to my original purchase to take something else .