I sent a phone back to the seller because it was faulty and 5 months later they still haven't fixed it. I've bought another one in that time, and now I've asked them for a refund as they have done nothing for 5 months they don't want to refund it; they want to send another. Can I force then to refund it? If not, and I now need to sell one of the phones, can I invoice them for the difference between what I paid and what I sell it for, as I'm out of pocket?