Buyer Opened Not as Described Case

I sold a 9ct gold pearl necklace and bracelet set on a different account and the buyer has opened a 'not as described' case saying the string under the necklace and bracelet is silver not gold.  I still have the original receipt for the bracelet (but can't find the necklace receipt) which clearly states 9ct gold pearl beacelet and I think they are also hallmarked.  Do I have to accept the return and lose the Special Delivery postage costs both ways?  Would Ebay accept the bracelet receipt as evidence or will they just side with the buyer?  I don't want to end up losing the items as well but I think its unfair to have to refund when I havn't falsely described a silver necklace as gold.

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You must be 100% sure of your facts before taking any action.Buyer may be trying it on, as they have changed their mind, but No Returns (which I assume you have on your listings) means they have to invent a reason for you to have to accept the return. If what they claim is correct, and it should be easy enough to prove or disprove on return, taking legal action could backfire on you.