Unwearable shie

I bought shoes in oct that I only put on in dec. Keeper it for a "sunny day". Put the shoes on and with the first step after putting on thicker socks and made the laces tighter notice my heal keeps slipping out as of the shoe is to big. My first thought is it's a manufacturing defect on the shoe . Shoe is unwearable. Contacted them.explain I know about the return policy and all that but can you take the shoe back and make contact with the manufacturer telling them that the shoe is unwearable. They just simply tell me they can't because of the return policy. Now I am sitting with a unwearable shoe.. and how many other will now buy this shoe from them and experience this issue