A group that says it represents about 3,500 Central Maine Power customers has issued a letter to state officials demanding a more thorough investigation into customer complaints of inflated CMP electric bills.

Calling itself CMP Ratepayers Unite, the group said it sent the letter because of concerns that the Maine Public Utilities Commission’s ongoing fact-finding probe into the matter has raised more questions than it has answered. The group also said Maine officials need to provide “immediate relief” to CMP customers who believe they have been overcharged by the utility while the PUC probe continues.

The PUC responded to the letter in a statement Thursday, saying that its investigation will be comprehensive, and that it already has taken steps to offer relief and protection to affected CMP customers.

In an email to the Portland Press Herald, CMP Ratepayers Unite representative Patrick Milligan said the organization was formed, primarily through Facebook and email, by an ever-increasing group of concerned Maine residents. A Facebook group called CMP Ratepayers Unite had over 3,100 members as of Thursday afternoon.

“Now surpassing 3,500 members, we have come together to share our most pressing concerns,” Milligan said. “Many folks have complained to the MPUC and the (Office of the Public Advocate). We feel the pace of the investigation has been slow, and has posed more questions than (it has provided) answers.”

Many CMP customers are furious over a revelation that the company was not forthright about serious technical problems with its new billing system at a time when more than 1,500 customers were complaining of inexplicably high electric bills.

Portland resident Camryn Hansen, who joined CMP Ratepayers Unite on the recommendation of her residential solar panel installer, said she experienced a bizarre sequence of events regarding her CMP bills starting in December.

Hansen said that for three months she didn’t receive a CMP bill at all, and then all three bills eventually arrived on the same day, bundled together.

Her bills for December and January were for about 200 kilowatt-hours of power usage each, compared with her home’s average monthly usage of about 700 kilowatt-hours, she said. The third bill, for February, was for 1,400 kilowatt-hours, which Hansen said made no sense, because February was relatively mild, whereas December and January were bitterly cold.

“I was like, this is so ridiculous,” Hansen said. “How could I possibly go from 200 to 1,400?”

Northport resident and group member Johanna Strassberg said the amount of her billed energy usage fluctuated wildly during a period in which her family was not even staying in the home.

Strassberg said the family was away from the beginning of January until the end of March, and during that time their CMP bill doubled from January to February, and then dropped sharply in late March.

“I phoned CMP on March 30 and was told that it had dropped way down on March 26 which I can see, but nothing changed, since we were not even home!” she said.

CMP has nearly 550,000 customers in Maine. About 97,000 CMP customers saw their monthly bills increase by 50 percent or more in December, January or February over the same month a year earlier, according to information the power company has provided to state regulators.

Many customers have said their bills suddenly doubled or tripled at some point after CMP switched to the new billing system in late October. They also have complained of other problems, such as receiving multiple bills or no bills, and being erroneously dropped from the utility’s monthly auto-payment system.

CMP has acknowledged problems with the new system but has said it did not cause customers to be overcharged. The company said the likely causes were nearly a month of sub-freezing temperatures in December and January, combined with an 18 percent hike in the standard offer rate for electricity.

Following a Press Herald report based on memos, some confidential, that show CMP knew its new billing system was rife with problems, Maine Public Advocate Barry Hobbins urged the PUC on May 4 to elevate its probe into the CMP billing issue into a full-blown investigation with the legal authority to punish CMP if the company was found to have violated state law.

A few days later, the PUC denied Hobbins’ request and said it would instead continue on its present course.

On Thursday, Milligan said his group wants the PUC to follow through on Hobbins’ request.

A copy of the group’s letter sent to the Press Herald is addressed to several state officials including PUC Administrative Director Harry Lanphear, Maine Attorney General Janet Mills and Gov. Paul LePage, whom it incorrectly calls “John LePage.” CMP President and CEO Douglas Herling is also listed as a recipient.

The letter includes more than 40 specific complaints relating to CMP’s billing, metering, customer service and other issues.

In a statement sent Thursday to the Press Herald, Lanphear defended the PUC’s approach to the investigation and said the commission already has taken steps to protect CMP customers affected by higher-than-expected power bills.

“The commission’s staff is currently reviewing and assessing hundreds of pages of data and information provided by CMP,” Lanphear said. “Among other issues under review, the staff is examining the bills of a sample of the approximately 100,000 customers that experienced increases, to determine potential causal factors. The next step in the investigation is follow-up questions and information requests by commission staff.”

The PUC also has hired a consultant, Liberty Consulting Group, to conduct a detailed forensic audit of CMP’s metering and billing systems, Lanphear said. Liberty will audit and analyze the accuracy and timeliness of CMP’s metering, billing and related systems from end to end, he said.

In response to complaints that the investigation is taking too long and that CMP customers need financial relief in the meantime, Lanphear said the PUC already has taken steps to protect energy consumers.

“For any CMP customer whose usage for any month after October 2017 is 25 percent higher than the corresponding month from the previous year, and the customer has disputed the increased bill, the customer cannot … have their service disconnected for failure to pay the entire amount of the bill, provided the customer pays an amount that is at least equal to the amount of the delivery service bill issued for the same month in the prior year,” he said.