Did he ship it in one package or separately? If he shipped it separately than he has already paid out the money to the shipping company, nothing can be done at this point.
If they put the items in one package and the shipping cost less than what you paid, the seller does have the option of giving you a partial refund. But unless the seller already said in the listing or in a message that he would charge you less, it really is up to the seller on how to handle it.
You should always ask about combined shipping before you make a purchase.
