E-bay is red hot on "item not as described" purchases now and you have a very strong case. I'm pretty sure if you want your money back you need to start a dispute in the correct drop down option and the seller has to pay return shipping, alternatively you can contact the seller and try to resolve it amicably and perhaps gaining a partial refund would be best but this has recently been limited by e-bay/paypal from personal experience. Another way they are trying to stop people giving them millions of dollars in fees every quarter. Your situation is weighted heavily in the buyers favour.
E-bay do seem to change their policies as much as I do undies so this info may be out of date now.