Dear "Seller's name here"
It has been over 48 hours since I replied (see below)to your offer for a partial refund and you have not replied to my counter offer.
I do not want to have to escalate this dispute. As this error is not my fault, I feel the only fair solution is for you to refund the entire purchase, including shipping. As I said before, you should also pay for return shipping, should you choose.
Please reply to me within 48 hours (9:00 p.m. MST on Sunday evening) or I will assume you are not cooperating and I will have to file a claim for Buyer Protection and will have to leave negative feedback on for this transaction. I do not want to do this, but I will if I must.
Please advise me as to which course of action you would like to follow.
Respectfully,
"My Name Here"