Ontario's ombudsman is calling on Hydro One to "overhaul its corporate culture" and instead, focus on customers and transparency.

André Marin released his report on billing practices at the utility today.

He said his office was flooded with 10,700 complaints from Hydro One ratepayers about over-billing or estimated bills, and what he calls "outrageously bad customer service" as it scrambled to fix technical glitches with a new system.

He said as complaints grew, Hydro One deliberately kept problems under wraps, and deceived the electricity regulator and the ombudsman's office "about the extent and nature of the company's billing and customer service disaster."

Marin said "customers felt mistreated and abused when they tried to report billing problems to Hydro One."

Several of those customers are in northeastern Ontario. Marin's report said a Sudbury man received a bill for $19,152 in April 2014, after a long period of estimated bills. Marin said his office learned the man's meter was replaced in November 2013, but it took four months to update the system. Marin said once the error was corrected, the bill was reduced to $74.

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André Marin is the Ontario ombudsman. (CP File)

Another example from northeastern Ontario was a Schumacher man who was "dumbstruck" in June 2014 when he received several bills totalling $45,000. Marin said the man contacted Hydro One and was referred to a manager whom he found "arrogant and uninformed." Eventually, the utility contacted him and explained that due to a mixed meter issue, he was being billed for electricity used by a nearby gold mine.

In an interim report in March, the ombudsman said Hydro One deliberately deceived customers by threatening to disconnect electricity for unpaid bills, despite its policy never to do so.

Marin also warns his office and Ontario's auditor general will lose oversight of Hydro One once the Liberal government's budget bill passes, approving the privatization of up to 60 per cent of the electrical utility.

"When the technical problems sparked a flurry of erroneous bills and a flood of calls from frustrated customers, Hydro One reacted in the worst way possible, with deflection and deception," Marin said.

"It minimized the issue, misled its overseers, relied on public relations spin and put its customers last."

'Focused on fixing technical issues'

In a statement, Hydro One president and CEO Carm Marcello, said he agrees with the ombudsman's recommendations, and added the utility is already taking steps to fix billing problems.

"We had a problem with our billing system, and we focused on fixing the technical issues," he said.

"But we failed to appreciate how our actions would affect our customers. We let them down and then we didn't treat them well when they had a problem."

Marcello said the utility has fixed the billing issues, has provided better training for staff and made customer-centred thinking part of every project.

With files from The Canadian Press