Return policy nightmare

I bought a wooden base from them on Thursday and it was delivered on Friday. I called on Monday to exchange it for something else as it was too big for the room and they said they will get back to me but its Wednesday and they haven’t said anything . I was told that I cannot exchange it as it was already assembled, my question was what is the return policy? And how was I suppose to know how it will look without assembling it? I am so unhappy because I explained that I will exchange it for something else in the store. The base was unused.