There is nothing you can do.

To repeat what has aready been said, if a buyer opens a return because the item is not as described, you have to accept the return, get the item back and refund the buyer.  Otherwise, you are likely to lose your item and the money.

If, when you get the item back, it is a false claim, you can report the buyer to Ebay.

You asked where it says this,  The link below will give details of the Money Back Guarantee for sellers but this is the relevant sentence and it is very clear and unequivocal:

I don't accept returns, why am I getting a request from the buyer?

If the buyer is asking to return the item because it's damaged, faulty, or didn't match your listing description, then you need to accept the return.

https://www.ebay.co.uk/help/selling/managing-returns-refunds/handling-return-requests?id=4115