I cancel the sell post 48 hours. I add them to my block list, relist the item, and simply move on. I spent too much energy on this situation the first time it happened to me.
And a final update : one buyer finally paid yesterday and the other overnight. Thanks for all the good advice about how to handle this. Mike
hope it worked out for you, but definitely block them from ever bidding again, adn report them, that is what i do, hope it helps (reading this 9 months later)