With these Chinese suppliers, sometimes you need to negotiate in a diplomatic way. A good solution would be to buy a replacement from them at a discounted price and sell on your 36v kit so that the price you pay for the replacement is close to the price you get for the 36v one. I did that with a Chinese supplier once, but I can't remember what the item was. It might have been a hub-motor or something entirely different. I can remember giving them the Ebay link so that they could see what I got for it. In the end, nobody lost much, and it was a lot cheaper than sending back to China.
We buy these things from China because they're cheap and available. You have to be philosophical. In the long run, you're still better off dealing with them. I baulk at the prices some people pay from the UK, but then it's creating jobs for people, so you're sort of donating your money to a good cause, sort of like charity.