Same here. Bill is usually around €200 at this time of year but it's nearly doubled to €395.
Firstly, there's a 20% increase, and it's also been colder. In addition, my wife is pregnant and she's been at home more. Finally, my billing period covers the last 10 days in October, plus November and December.
I still think I'm being completely ripped off. I have spoken to quite a few people about this and everyone I've spoken to is in the same boat - ridiculously high bills.
I also rang Bord Gais about it and the girl on the phone said they'd be inundated with calls. I got her to send me out the key and took a meter reading myself (even though they said it was actual). There were no issues there - meter reading was as expected.