Unfortunately, that's the chance you take when you buy a Chinese spindle. Regardless of what they say, the warranty is most likely worthless. Even if they honored it, you'd have to pay nearly the cost of the spindle to ship it there and back.
With a new spindle. you can file a PayPal dispute, but that also might cost you the cost of shipping it back before you get a refund.
Are you sure you have all of your VFD settings correct? Did you open the spindle and check for water leakage? Chinese spindle failures seem to be pretty rare these days, and you'd be extremely unlucky to get two bad ones.
Other than rolling the dice on Ebay, you really only have two other options. You can by a Chinese spindle from an importer that will warranty it, like UGRA CNC, for about 50% more. Or by a non chinese spindle for 5-10x the price.
Actually, the cheapest option might be to make an offer for two spindles on Ebay to get a better price, and have a backup.