Hi billb, we had this problem last year when we switched to airtricity, but we actually received no bills at all. We contacted both companies to find that ESB no longer had us on their system and Airtricity had no record of us at all. We knew we had set up with airtricity because my brother worked for them so we gave it a couple of months and about five or six months later we got a bill for the last two months. We queried this and were told the bill was only in place two months, even though had contacted them about it before.
So what I'm trying (badly) to say is maybe they have made a big mistake and once you are still receiving power and notifying them about the situation there should be nothing to worry about