Is it too late to enter a resolution process?

[bom351]

I bought an item 6 months ago from a seller in China. The original item I received was faulty so we agreed that I would return the item and they would send a replacement and refund my postage costs. After a long period of waiting with periodic contact, only to be told it takes time for items to arrive, I asked them to send a further replacement. I am still without my item. I am still without a refund for my postage costs and I am now worried it may be too late to get a resolution to this at all (whether it be a replacement or a full refund). Any help would be greatly apreciated.