If you bought it from a Chinese seller, then you probably received a fake. Unfortunately, as it's more than 6 months since you purchased, there is nothing you can do. Even if the seller offered a warranty, it isn't worth the screen it's printed on. The best you could hope for is to take it to a local place that might deal with phone repairs. You won't get any help from eBay, PayPal, or the seller. Sorry.
In future, as tempting as cheap phones are from China, don't do it. If you want the newer models, Harvey Norman (and other places) offer interest free terms. Buying locally means if something does go wrong, you are covered by a warranty. You also know that if you buy a Samsung, that's what you're getting.
