If you email the seller be patient
they may have just made an honest mistake and will be willing to work with you.
If not your coin will be easy to sell and you can purchase what you wish with the proceeds.
I once sent the wrong item to a buyer and as soon as I realized it I sent the buyer the correct item and asked them to return the first item sent in error.
even though I sent the correct item within 24 hours, it took the buyer 4 months to return the other item to me.
So do not jumop to conclusions until you hear from the seller.
Best Wishes