bump and nova :

When a seller refunds a payment ebay then marks the transaction as refunded (unpaid). 

I know that when this happens a seller can lodge a mutual cancellation to recoup the final value fees for the refunded item but I cannot recall whether it is possible to open an unpaid case (hence my careful wording :.. if at all possible ...)  

An unreasonable buyer such as this is hardly going to agree to a mutual cancellation and it would be a shame for the seller to lose final value fees (albeit a small amount)    I cross my fingers that the OP might be able to open a case  

I did not suggest that refunding would stop the buyer from leaving bad feedback -- sadly there is no way to avoid bad feedback in this instance.... let's hope the buyer is the type who doesn't bother with feedback

Hope that clears up any confusion you had 🙂