As temperatures drop across the U.S., the number of scammers posing as heating or electric companies is on the rise.

Utility-related scam phone calls soared 109% in 2016 and are expected to continue to rise as cold callers become more creative in fooling an increasingly savvy public, an analysis of 3.5 billion monthly calls and texts from spam protection service Hiya found.

“If you find yourself on the receiving end of one of these calls and you’re not sure if it’s legitimate, hang up and call your service provider, in this case the number on your local utility company’s website or bill,” said Jan Volzke, vice president of reputation data at Hiya, which picks up calls automatically and blocks numbers that have been reported as telemarketers, robocalls or scammers.

Here’s how the scam works: Most often fraudsters will solicit personal and billing information on calls telling a consumer they are eligible for a federal program or will offer to lower a utility bill. Once they get the information, they can steal the victim’s identity and open accounts in their name. Another scam involves threatening to shut off a consumer’s electricity unless they immediately make an overdue payment, directing them to an 800 number. Victims have sent money via prepaid debit cards, wire transfers, and other forms of payment that cannot be traced back to the scammer, and have lost anything from $50 to $2,500 in these scams, the company found.

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The top five companies scammers claimed to be calling from are General Electric GE, -0.22% , Duke Energy DUK, -0.26% , ConEd, Georgia Power, and Consumers Energy. And the most common area codes these calls come from are 508 (Massachusetts), 201 (Hudson, N.J.), 914 Westchester County, N.Y., 323 (Los Angeles), and 330 (Akron, Ohio).

If a consumer suspects a call to be fraudulent, they can file a complaint with the Federal Trade Commission as well as their state’s attorney general office, a spokesman for the FTC said. “We suggest that consumers who get calls from anyone who they doubt are actually with their provider, they hang up, do not engage with the caller, and call back the main utility customer service number to see if they actually were trying to reach them,” he said.

Many consumers aren’t aware of these utility scams, even though they may be on their guard for other common telephone scams, said Alex Quilici, chief executive officer of smart call manager YouMail, which blocks robocalls and tracks scams. “The phone utility scams are a new one, at least at scale, so they aren’t as widely known,” he said. “People know about cruise ship scams because of the sheer volume of those scams – it’s likely they’ve gotten a voicemail from one, which makes them aware of it.”