cancel purchase

[lfm72]

A buyer asked me to cancel purchase after payment is made and shipment already at post office. I initially refuse to cancel purchase since I think that I will be unable to stop the mail but I finally manage and retrieve package and  therefore confirm to buyer that I can now cancel purchase....I relist item and it sells immediately to a new buyer!! (I mail it the next day to the new buyer). I still unfortunately have Ebay that tells me I cant cancel the purchase and Ebay keeps telling me to mail the item (I had originally purchased postage at the post office not through ebay/paypal). I do not want to make the first original buyer wait for a refund I send the refund to them directly through paypal but the BIG ISSUE NOW IS CLEARING THE WHOLE MESS ON EBAY......How do I cancel the purchase? I will be paying seller fees on the item that sold to the second buyer but since the first buyer got their refund and never got the item I NEED TO CANCEL THAT ENTIRE SALE...I am going crazy trying to do this without any success......any suggestions please???? Thanks so much for your help!