If your instincts are to reply OP, then you should.
Like other posters, I also liked the suggestion by ImTooHecsyForYourParty (19:36:43). There is a change I'd make though, I'd replace the final line of:
Please do not contact me again.
with something like:
As far as I'm concerned the matter's now closed. Therefore, I hope you'll understand that I don't want to enter into a discussion about this.