Admited a few year back and pre the RWE takeover, but my partner has the same issue as this..
We had a series of demanding letters and our details sold onto a debt recovery firm for a £750 N-power bill we did not owe.
We both WORKED for npower @ the time, and even though Npower accepted that there was no bill, the debt collection agency kept hassling my g/f (saying they had not been told to stop). It went on for ages, because we worked for them, we were actually able to get in touch internally with managers and had an apology & flowers off the top man @ the time. A few weeks later.. it started again… eventually after a load of stress, Npower finally admitted they owed the g/f money not the other way round… Muppets total muppets