Sellers can't refuse to accept returns on defective items if you open a case within 30 days of receipt and choose the right reason for return.
So, when did you receive your item and what reason did you give for returning it?
EDIT: If it was the item bought on 2nd december, it looks as if you simply left it too late to start a return. You only get 30 days - no exceptions.
You could try your payment provider.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)