Store manager refuses to exchange shoes for me

I bought formal shoes on the 03.12.2015 and find out that this shoes doesn't fit me well after wearing them 3 days thinking that they will stretch but it didnt,i went back to Markham on the 09.12.2015 to exchange and take bigger size or replace it with other shoes but the store manager advised that i cant exchange the shoes because i wore the them, i find it unfair as a customer because is the same shoes that i need to wear everyday to work,my toes get swollen after wearing those shoes.I will be very happy if they allow me to exchange this shoes and take the one that will fit me well.