Bought a faulty item and only got partial refund ? Any advice ?

[fakeblondie]

I bought a lamp for dd bedroom for 16,50 and postage was 4.00 so 22.50 altogether.
lamp arrived obviously not as it should be so I took several pics and returned to sender .
he has refundede me 16.00 .
So I am 4.00 postage out of pocket plus the 3.50 it cost me to send it back which is 7.50 plus . 50 which is 8 pounds altogether.
it was a fibre optic light display for dd nursery and was completely lopsided . there is no way I would use it.
Why should I be out of pocket for paying for a faulty item ?
If I open a case with eBay will that mean I can't leave feedback ?
Any suggestions welcome please.
I know it's not much money but its the principle that's annoyed me. He did offer me a tenner refund and keep the lamp and I said no because it was completely broken !
TIa

yes open a case to get a refund of the balance of £4 - the £3.50 return cost you can't force the seller to give you unfortunately

and yes you can still leave negative feedback and low stars

Thank you thats very helpul.