More people are having problems paying for power than three years ago, Consumer New Zealand has found.
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Its survey found 25,317 homes had power disconnected last year because of unpaid bills, compared to 19,106 in 2015.
Last year, 18 percent of consumers had had trouble paying for power.
Consumer's head of research Jessica Wilson said the figures were really concerning,
"Electricity is a basic consumer right," Ms Wilson said.
"Everyone should be able to get access to affordable electricity and decent service.
"We're in the middle of a real cold snap - if you're struggling to pay your bill and if you're cutting back on heating, really the market isn't delivering for consumers."
The survey also found many customers were unhappy with the service provided by pre-pay retailer Globug, with 42 percent saying they'd had bad experiences in the past year.
Those who used the provider were usually vulnerable people on low incomes, who other power companies wouldn't take on, Ms Wilson said.
"These are people our survey found are already having trouble paying for power costs. The fact they're also getting bad service ... is really concerning."
One in four Globug customers said they had complained to the company about its service.