Can I just ignore a "Transfer to collection agency letter"?

I am having an issue with Bord Gais. My wife had handled all our bills but she passed away a few weeks ago. When I went to sort out our account with bord Gais they said they couldn't talk to me because of the freedom of information act. She's the named person on the account. Even though my name is on the bill too. So what I did is setup my own account and canceled hers. They said I would need to pay what was left on that account. I had recently paid the old bill so there was only three weeks into the new cycle.

When the bill came it was for nearly two thousand euros. Clearly a mistake. We average about €150 at most I've been on to them three times. Which is pain because you're on hold for almost an hour each time. They agreed that it was a mistake. I followed their instructions and emailed them twice with a timed stamped photo of the meter. I've even sent a web texted asking if this has been sorted. I heard nothing back. But, now I've received a letter "Transfer to Collection agency/ solicitor. In the letter They claim THEY have contacted me on a number of occasions. They haven't. I going through a lot of grief at the moment and don't need this shite.

My question is because she is the account holder (even though my name is on the letter too) Should I just ignore it at let them go after my late wife or am I accountable?

Thanks