If it is on a subscribe and save offer you cannot return it, however, I had some tablets for my dog on S&S and they arrived a week after my dog was put to sleep, I tried to return them but Amazon said no, I contacted customer services and eventually managed to speak to a real person, I told him that I was not happy with this because there was no way of knowing beforehand that I wouldn't need them, £60 was a lot of money to me and Amazon need to have something in place for situations like this, he told me that he could do nothing but he would ask his manager.
Result, I was given a full refund and they said that I could dispose of the tablets