I am being harrassed by a buyer, that I offered a refund to, left him positive feedback, can it be taken off?

How did you sell the same item twice on the same day? And for the exact same price? Why do you want to remove their positive feedback that you left?  Some aren't as forgiving as others.  Looks like you ran into the latter.  You may be able to block their emails but I am not sure how to do this.  Did you apologize in the first place?  Not that I condone harassment but I would also suggest that you treat your customers fairly and own up to your mistake and the way you wrote this shows that you may not have understood that a customer's time is valuable and they may have felt taken advantage of. But I may be missing part of the puzzle on this one.