Cancel an order

[nfwb11]

SELLER QUESTION:

Someone won an auction of mine and then asked to cancel the winning bid.  I don't believe it was a mistake, simply buyer's remorse, and responded that I would not cancel.  I still think the buyer is acting in "bad faith" but have since reconsidered and would like to cancel the sale (again, I am the seller) but since I already responded "no" I cannot do anything else... other than try and get through to ebay.

Can I do this without calling them?

Thanks!