A woman whose company was landed with a $24,000 electricity bill after months of under-charging has won a 50 percent reduction in her debt.
The consumer watchdog, Utilities Disputes, found the electricity supply company didn't check its billing and ignored information provided by the customer.
The under-billing had dragged on for more than a year before a single invoice arrived with a giant catch-up clause.
Attempts to settle the matter by negotiation were unsuccessful, and Utilities Disputes Commissioner Nanette Moreau investigated.
She ruled the final bill should be halved, saying the electricity company didn't take action to confirm its billing was correct.
Nor did it use information provided by the customer to address the problem.
Neither the electricity provider nor the customer was named in the report.
In another case, a man complained that a distribution company had used incorrect data to calculate his bill.
This ended with $550 credited to the man's account, even though the company rejected any blame.
Not all complaints were successful, however.
In another case, Mr F complained an electricity outage damaged a modem and other electrical equipment, but the Commisioner ruled that the power failure did not cause the damage.
Utilities Disputes, formerly the Office of the Electricity and Gas Commissioner, provides a free mediation service for people whose complaints with gas or electricity companies are deadlocked.
The annual report showed that 5534 cases came to its attention and most were settled between the utility company and the customer.
But 225 went on to be decided by the commissioner. Of these disputes, Trustpower received the largest number of complaints among electricity retailers, at 32, followed by Meridian Energy.
Vector was the worst perfomer among lines companies, with 31 complaints, and that was a high number of complaints relative to the size of its market share. Powerco had the next largest number but proportionally, it performed better.
Utilities Disputes also looked at its own performance, and found it met only one out of three required standards for timely attention to complaints.
It blamed one very complex case for these delays.
It also said electricity and gas companies were very satisfied with its performance, while people making complaints were less happy with the way the organisation worked.
Utilities Disputes is reviewing the way it works.