No one here can deal with this, as we are members like yourself, with no access to your account or to the items sold.
However, we can best advise how to proceed.
First I would send the buyer a polite message, you can add photos of the item you sold, and ask if perhaps they have mixed you up with another seller, as from the photos, it is quite a different item which was sold.
If they disagree and carry on with an item not as described case, you will have to accept it, as cases are all automated, no human contact, so no point challenging it at that point.
Accept and pay for the return tracked postage within 3 days, that way your seller fees are refunded, and your seller peformance not affected.
Should a diifferent item be returned to you, then muster all the evidence you have, photos will help, and appeal the decision for the refund, citing the buyer has abused eBay's 30 day MBG policy to receive their refund.
If you need to, this explains how to appeal:
https://www.ebay.co.uk/help/selling/manging-returns-refunds/appeal-eBays-decision-return-missing-ite...
