I presume you paid via Paypal in which case as you'll have to return the phone to the seller, you will need to lodge a dispute with Paypal so that they can give you the correct address to which you must return the phone.
Do NOT return it to any address other than that provided by Paypal, and remember that you must first also remove the Li-ion battery before sending the phone back to China as they are prohibited goods and cannot be sent anywhere by air mail.
Also, when returning the phone only, do so via Registered Post International which is the postal method recommended by Paypal. This will cost you approximately $22 of your own money and is an unrecoverable added expense.
There's no way the seller will replace the phone without receiving the original one back first so if you absolutely must have a phone for medical reasons, just buy yourself a $24 cheapie from Coles for use in the interim.
I don't know what you originally paid for your Chinese phone, but bearing in mind that the cost of buying an interim replacement plus the cost of returning the unsuitable phone to China will set you back a minimum of $46 or more, you really need to ask yourself if it's worth all the expense and effort of doing so, especially as there's no guarantee that the replacement phone will be any better than the original.
