Susan Strafford faced rising gas bills, even switching suppliers, over a three-year period before finally being notified her meter was still charging her imperial measurements - essentially double the price - despite being switched over to metric.
She wants to warn others the same thing could happen to them.
Mrs Strafford started paying a Â£75 per month with OVO when she moved into her terraced house on Harris Road, Hillsborough, in 2013.
It soon went up to Â£80, then Â£105 in July 2014.
She switched suppliers to NPower, who were offering Â£80, but soon, the bills were on the rise again, back up to Â£80 per month, which was being taken straight from Mrs Strafford's account.
She said she knew something was wrong, but both companies' policy was to charge Â£90 to look at the meter.
Meanwhile, she continued toughing out the cold winters in the house she said was built in 1901, and which offered precious little insulation.
"Most of the time, I'd go to bed early, because it was warmer in the bedroom," the 66-year-old said.
"I've been extremely upset, worried that I'd be unable to put the heating on, or I would be unable to put the hot water on."
After countless phone calls - she estimates she rang 40 times - she got the ombudsman involved.
That was when it was discovered that the system was still in imperial.
Mrs Strafford has been refunded by both companies - Â£870 by OVO and Â£825 by NPower - and said Sheffield people might not be aware they were being overcharged.
"I had no idea about metric or imperial measurements at all," she said.
She urged people to check with their supplier to make sure the settings were correct.
"If there's something wrong, you need to have a look," she said.
"It could be imperial instead of metric."
She said she was relieved her ordeal was over and she could afford to heat her house again.
"It hangs over you the whole time," she said.