Ever changing Return and Refund policy

I bought a sale item that was on 30 days return. When I wanted to return the item within the 30 day period, the refund was rejected because now suddenly the item was on a 10 day return. I called customer service but got nowhere. On the email they send you when you buy the item, they only add the return policy, but not what part of it applies to your item. Some sale items say 30 day return and some not. Then, at the time where you want to return it they say no it was on a 10 day return and you have no way to prove it. It would help if they put on the email that they send you, whether the item is classified for returns and what the period is. It is not fair that the policy changes like the weather. Will not buy from them again.