More than 2,000 National Grid gas customers have received bills for thousands of dollars more than they owed -- including one for more than $30,000 -- over the past year because of billing errors tied in part to computer problems.

The company this week acknowledged the problem and said it was working to resolve the thousands of overcharges by the fall. The company last year was fined $8.9 million by the state Public Service Commission in part because of excessive complaints.

Gerald Gralton of Riverhead said he knew something was wrong when he started receiving monthly natural gas bills from National Grid as high as $6,400, including for winter months he was in Florida.

VideoNational Grid: Meter bug overcharged thousandsStoryNational Grid fined $8.9M for missing targets

"It went on probably for a year," Gralton recalled. He said he complained and he tried to fix it.

Marvin Levine of Albertson was caught off guard when his normal $200 bill for natural gas came in at $9,200 in April. He had signed up for an energy service company, or ESCO, over a year ago, but the bill was switched to another company without his knowledge, he said. He's now back with National Grid. "They said, 'We're not going to charge you until it's settled,' " Levine said of National Grid.

Gralton and Levine are among more than 2,000 of National Grid's 570,000 Long Island customers, and of energy service companies that National Grid supplies, who have seen bills skyrocket because of computer system errors over the past year.

advertisement | advertise on newsday

National Grid spokeswoman Wendy Ladd said the company was "actively resolving two specific issues that have caused billing issues for some of our customers."

James Denn, a spokesman for the state Department of Public Service, said the office's consumer advocate is "aware of and has been investigating the billing problem" at National Grid.

He said the department had been "assured by the company that the majority of the incorrect bills have been resolved, and those that are remaining will be resolved." National Grid's responses to complaints "will be monitored as part of the investigation," he said.

Ladd said the problems stemmed from National Grid's separating from LIPA last year. The change required a new billing system and call center, she said, and National Grid began installing new automated meters across the service territory to replace meter readers who stayed with PSEG.

Ladd said that during the billing system conversion, "there was a system issue in syncing customer billing data with ESCOs for their billing use."

At the same time, National Grid experienced "programming errors" with the more than 500,000 new automated meters, which send out a radio pulse that allows meter readers driving down a street to collect usage data automatically.

Ladd said the company was "on schedule to stabilize the system and reconcile all accounts by the fall."

Carol Sykes of Patchogue said National Grid admitted mistakes with a gas bill that spiked to $30,587.07 for the April-May service period in 2014 for her 2,000-square-foot Cape Cod house in Patchogue.

But in the end, a manager said she still owed $4,000. Her typical bill had been around $150 a month. She said she signed a statement saying she'd pay off the $4,000 at $10 a month, because she couldn't fight anymore.

"I lived in fear," said Sykes, whose husband is awaiting a liver transplant. "I was getting calls from their collection service, told that my gas would be turned off. It was a big nightmare, it was really, really horrific."

advertisement | advertise on newsday

Ladd acknowledged the original bill and said Sykes was given a "sizable credit," but still owes more than $3,600 for gas she used.

Another customer, Faisal Zakaria of Jericho, received a bill for $4,493 in April, more than 20 times his normal $200 monthly bill. He said the company was initially slow to resolve it, and did so only after Newsday intervened. National Grid said his problem has been resolved completely.

Ladd said customer calls about the issue have been "trending downward" in recent months, and that National Grid had "exceeded our customer satisfaction-rate targets for the past seven months."

Last month, National Grid was fined $8.9 million after the state Department of Public Service found the company missed two state performance metrics last year: total complaints received and customer satisfaction.