mixed up goods being given

I put my laptop plus charger in a buy back as I needed funds. But when I went to collect my item, I was given a different charger that wasn't mine neither could it charge my laptop. Meaning that while your items are in buy back, it's being used by the staff. Hence it being the wrong charger given. Staff is telling me that there's nothing they can do about it as they don't know where my original charger is. So now I have to settle for a charger that's not my original one and that's not working.