I'm not sure if you're aware, but there is a card called Antimatter that does exactly what you describe: turns your creature's attack into an equal heal.
As for him not responding - PvP itself has more bugs than Starship Troopers. It's likely that he wasn't getting your messages - or you weren't getting his.
Or maybe he just didn't want to bother responding to some whiner crying 'Hacker' with no reason.
I could be wrong, just my opinion.