Not satisfied with the response on my exchange que

I bought summer shoes online in July, while it was still winter as they were on sale. Received my shoes and I loved them but I never wore them as it was winter. Now I tried them on and I realised they were too big, should have bought a size 3 instead of a size 4. I have not worn them, they are still new. I contact take a lot to exchange them to a smaller size. They told me they cannot exchange as it's over the period of 30 days. So what must I do with big shoes, worst they didn't even collect the shoes to inspect them to see if they were still new, they just declined my request. They must exchange this shoes please.