When you attempted to install the part did you change it in any way?
This can include opening a sealed box.
Contact the seller with your question.
It is best, particularly if the seller is overseas, to accept a refund rather than wait for a replacement, which may be no better than the original or never arrive.
The seller may want the original part returned. Use a Delivery Confirmed service. This can be expensive.
If the seller is not helpful, you can start a Dispute through Paypal. PP will require you to return the item with Confirmation of Delivery. Once PP sees the item is returned (not shipped , recieved) they will refund you and go after the seller for the money.
HOWEVER- the seller is not required to accept an item that has been changed in any way.