OK, so this was a used item that they did not fully inspect before putting into stock and shipping out. At this point, you have a collection of spare parts for which they charged you intact-item price for. If you haven't already, send them that image and demand a refund WITHOUT having to ship anything back since the item is useless as-is. OR demand a pre-paid RA label. I agree that you should not have to pay return postage to ship it back.

However . . . how absolutely cheaply can you send it back yourself (i.e. - - in a bubble or tyvek envelope or something)? If you can for, say, under 3 or 4 gbp, you might just want to lick your wounds and do it.