A Belfast man said he got a terrible shock when Electric Ireland presented him with an unexpected domestic bill for over £1,200.
Terry Corr (64) spoke of his anger and worry over the outstanding debt because he believed he had been paying enough by direct debit every month to cover his power consumption.
The freelance creative, who currently works part time, also said he decided to speak out publicly "so that others could potentially avoid the same expensive pitfall".
"I'm still trying to get my head around being told I owe a whopping £1,217.87 for electricity I was convinced I'd been paying for all along," he said. "To say it came as a complete shock to me is an massive understatement."
Electric Ireland told the Belfast Telegraph that "the bills in this instance have been accurate and in accordance with meter reads".
Mr Corr said he received the huge bill following a recent move from a semi-detached four bedroom house in south Belfast to a new property in the east of the city.
He said he believes the problem arose when he switched electricity supplier in 2017.
"Electric Ireland suggested that perhaps I'm in arrears because I failed to keep up payments," he said.
"This made me furious as I always pay my way and I had been paying them £41 a month.
"I'm not disputing that I used the electricity. What I'm saying is that I made monthly payments to them in good faith without realising that a bill time bomb was about to go off through no fault of my own."
The family man said he had trusted Electric Ireland to keep him informed of his usage.
"I honestly never queried their charges and I believed they would inform me if and when they needed to increase the monthly payments," Mr Corr said.
"They finally offered to take 35% off the outstanding bill and said that this was non-negotiable."
Mr Corr said that while he "accepts some responsibility" for running up the bill, he thinks 65% is "very steep".
"They've now suggested I set up a direct debit to pay back the 65% debt over two years, which works out at £40 per month," he said.
"I feel they should reduce this figure and accept that they have failed me by not communicating with me properly."
A spokeswoman for Electric Ireland said consumers should call the company "to amend payments" so as to "remain in control of what they are paying" and "budget accordingly".
"When a customer switches to Electric Ireland and chooses to pay by direct debit, the monthly payment amount is based on usage over a previous period and is agreed with the customer and a company representative," she said.
"It is explained at this point that this is an estimate and that a reconciliation process will take place and adjustments will be made if necessary.
"The customer then receives quarterly bills via their requested channel, by email or post.
"The bills in this instance, have been accurate and in accordance with meter reads."
The spokeswoman advised householders to monitor their bills and payments.
"If a customer sees a balance accruing on their bill, they can call Electric Ireland at any time to amend payments either up or down," she said.
"This way customers remain in control of what they are paying and can budget accordingly."
Electric Ireland added that it "seeks to support customers in their individual needs" and also offers "alternative payment options including pay as you go meters which customers can top up as needed".
The spokeswoman also said: "We would encourage all our customers to look at bills when they arrive and to contact us immediately if they are facing challenges in meeting their payments."