You do realize your giving even more reasons to reply. I want this to stop just as much as you do but I don't like insults being left unanswered.
Sometimes you just have to let things happen even though you feel it's wrong. If you want it to stop, then do like you would with a fire and let it die out. Your replies are just fanning the flames.
Your two best bets are to apologize, or just stop replying. Trust me, it only ends in ruin own the path you're going down.