(CBS SF) — Criminals purporting to be PG&E employees are targeting North Bay and Northern California residents in a telephone scam, the utility said Monday.

The callers threaten to shut off power if a cash payment is not made immediately on a utility bill with a cash card, PG&E officials said. The bogus calls have doubled in the past year. Petaluma police on Friday also warned PG&E customers about the scam.

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Most of the incidents reported to PG&E happened in Marin, Sonoma, Lake, Mendocino and Humboldt counties, according to PG&E.

The scam calls also are becoming more detailed. The caller uses specific names of customers and guesses the general amount of money the customer owes. They also disguise their true phone number with a caller ID that says “PG&E” or “Pacific Gas and Electric,” according to the utility.

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Some scammers notify residents they are eligible for a federal tax refund related to their utility bill, try to sell services related to solar evaluation or claim to represent a PG&E initiative to sell a product in an attempt to gain access to the customer’s home.

PG&E does not ask for personal information or a credit card or checking account number over the phone, and anyone who did provide one to a scam caller should report it to their financial company and law enforcement.

Customers concerned about a call regarding a past due bill, service request or request for personal information should call PG&E at (800) 743-5000.

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