I cannot really add anything to the general thread of this page. I just wanted to add to the weight of evidence of how poor they are. Everything written by suffering customers, I have experienced too. It's a very familar tale, as I read everyone's comments.
Poor poor poor. No correspondence, keep your money when in credit (and still have my money), our billing systems are 'having problems' is regulary used by customer service teams. Complaints never responded to and good luck to you if you need a final bill producing. My new online account didn't work, still no resolution. I was told to wait 28 days for a web team resolution. This caused me to be unaware that they had made up some arbitary direct debit amount on my account. Incorrect direct debit amount, no-one could tell me why it was the figure it was. The 'experts' at Npower, the ones who could maybe actually sort out our problems, are 'not customer facing' I was informed by some dis-interested service advisor. Stay away, far far away from this company