The fun never stops eh? Although this is on behalf of a relative, not me this time.
As succinct as I can keep it:
1) Relative joins nPower January 2013 shortly after moving to a new property
2) Meter readings provided - nPower setup a monthly direct debit for £65 (dual fuel)
3) Relative became aware in June '13 that account had been setup incorrectly. Relative was only being billed for electric.
4) Took a couple of days to sort and more than one phone call, but a new direct debit of £90 was setup. This included the arrears as a result of nPower's mistake.