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(CBS) — You get a call from your credit card company asking if an unusual charge is really yours. That’s become an effective protection from identity thieves.

As 2 investigator Pam Zekman reports, they’ve now found a way around it.

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It’s called “porting.” Legitimately used, it’s a convenient way to transfer your old phone number to a new phone and carrier or home. Illegitimately, it’s being used by identity thieves to facilitate fraud.

Richard Poethig found out the hard way. The 90-year-old grandfather got a phone call from a woman who said she was conducting a survey about television programming for children, a topic that interested him.

“They asked me three questions all related to children and watching TV, and she kind of caught that I was an older person therefore I had a grandchild,” he says.

He responded to the questions.

“`Now,’ she said, ‘you have to hit the 9 because we’re going to record your answers.’ I did,” Poethig recalls.

All of that led to his losing his phone number on his AT&T landline in his home.

“I lost a lot of other things as well,” Poethig said. “I lost my identity.”

What happened? Identity thieves transferred the phone number to the thieves’ cell phone, a prepaid T-Mobile cell phone.

Federal Communications Commission porting rules are vague and confusing when it comes to what carriers must do to validate a request to transfer a phone number. And the rules require the transfer to be done in one day.

To stop it, experts like Governors State University Prof.  Bill Kresse believe the rules need to be tightened.

“In trying to balance the convenience to the consumer and the interests of the telephone companies, they’ve made it easy for bad guys to exploit the system,” Kresse said. “And that’s the key to this whole fraud.”

Also key: The fraudsters had Poethig’s Bank of America credit card information, and records show they charged more than $14,032 to the card, mostly for untraceable prepaid cash cards. The largest amount — $9,623 — was spent at a Walgreens.

“How in the world can anybody charge $9,600 at a Walgreens?” Poethig asks.

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Bank of America red-flagged some of the charges and called the Poethig phone number listed in their records but apparently reached the crooks on their cell phone. So they wound up telling the bank that the illegitimate charges are really legitimate.

“Once the bank thinks they have been told by consumers that these charges are legitimate they will take down the protections and allow that credit card until it reaches its limit,” Kresse says.

Bank of America finally reached the Poethigs by mail, inquiring about the charges. When Poethig told the bank they were not his, the bank cancelled the couple’s old credit card, gave them a new one and is not holding them responsible for the charges.

Kresse says the scam is an example of fraudsters being one step ahead of reforms.

“And this is going to take off like wildfire,” he says.

AT&T and T-Mobile say they follow FCC rules.

A T-Mobile spokesman said the company doesn’t require a customer name, address or Social Security number for the prepaid accounts. However, AT&T has to validate the information provided, and in the Poethig case, AT&T only required that the customer’s account number was verified in order to authorize the port over to T-Mobile.

“As such, the unknown person had access to the customers AT&T account number,” the spokesman said. “Additionally the order took place  on line and  T-Mobile did  not have any direct contact with the AT&T customer.”

A spokesman for AT&T said: “Per the FCC requirements, necessary documents from the wireless provider indicated they received customer authorization to port the number. We must then complete that port based on the accuracy of the information provided.”

After CBS 2’s enquiries, the two companies arranged to restore the Poethig family’s phone number back to their AT&T account.

In a written statement the FCC called this “an alarming instance of fraud,” adding “The FCC is always concerned when consumers are defrauded or scammed.”

The case is now under review along with more than a 100 other porting complaints.

Meanwhile, the FCC says that if you suspect you have been a victim of a similar scam you should contact your  phone company, file a police report, and contact your bank and other  financial institutions. You should also file a complaint at FCC.gov/complaints or 1-888-Call-FCC.

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The Illinois Attorney General and Chicago police are also investigating.