It's pretty clear-cut under the Consumer Rights Act, which is what Sale of Goods is called these days; if goods are rejected (eg because not as described), "the trader must bear any reasonable costs of returning [the goods]".

Money Claim Online (which is what Small Claims is called these days) is quite painless, but you do have to be willing to follow through because you'll pay postage on your Letter before Action and you'll never get _that_ back without going through the process where you launch the claim.