Look at it from their point, you asked for a product, they helped you out, supplied something that will work, later you decided you don't need it anymore, for whatever reason, not that the item they supplied was faulty, so in essence they need not refund you. You are actually just asking them to do you a favour, they don't want to, their choice....
I understand where you are coming from, but if I supplied an item to somebody, the transaction is completed after he/she has paid, anything after that becomes a new transaction, where I have the choice to supply or not.