Contact the seller and explain your problem.
Ask for a Mutual Cancellation on the unwanted item. When the request shows up in your email, agree immediately. Leave positive feedback.
Since English is not your first language, here is a suggested message to the seller.
I apologize. I purchased (item number & item title) twice, but I only want one. I have paid for the first purchase. Please send me a Mutual Cancellation request for the second. I will accept it promptly. Thank you for your help. (your real name)
