NEW YORK (CBSNewYork) — A Con Edison billing mistake cost a Brooklyn woman thousands of dollars over several years, and no one can explain how it happened.

As CBS2’s Tracee Carrasco reported, the woman issued a warning Thursday night so others can avoid being victims of meter mix-ups.

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Every month, Aleksandra Spyra received her Con Ed bill – an average of $159 for the two-bedroom apartment she shares with her boyfriend and toddler in Prospect Lefferts Gardens, Brooklyn.

“This is a large apartment, and I thought that the old air conditioning plus my large refrigerator and you know, watching TV all day — I thought that’s it, that caused my high bills,” she said.

It was not until September when Spyra received a Con Ed notice alerting her that she was using 117 percent more electricity than her neighbors.

“I was like whoa, how is that possible?” she said. “I’m extremely frugal.”

Spyra called Con Ed to come out and investigate.

“Any chance I’m not paying for two apartments, maybe hallway, maybe something?” she asked Con Ed.

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A Con Ed representative discovered the problem. For the last eight years, Spyra has been paying for her upstairs neighbor’s electricity – an apartment with four adults and several more appliances.

The mistake cost her roughly $10,000.

“She basically told me that well it’s nobody’s fault; it just happens,” Spyra said. “So I asked, ‘What do you mean it just happened, like you’re saying it as if I picked the meter when I moved in?’”

A Con Ed representative told CBS2 it is not clear how the mix-up happened, but the meters did pass inspection years ago when work was done in the building. Spyra wonders how long it could have gone on, and now worries that it may be happening to others who may not even realize it.

“I feel like every month, I just go and hand someone a check, basically,” she said. “When I think about it, it makes me very angry.”

Con Ed told CBS2 it is in the process of calculating a refund for Spyra. She will be repaid with interest for the meter mix-up.

Con Ed said if you have access to your meter, you can check your service by turning off all your appliances and lights and looking to see if your meter is advancing.

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Con Ed will also come out and verify if service is needed.