Marcy Troy was thinking about buying a new telephone, so when she saw an advertisement for new phones in her December Verizon bill she ordered one. It was easier than driving to the mall. And who better to order a phone from than the telephone company? Just make monthly payments on the phone bill.

Troy didn't like her new phone. No problem. Verizon exchanged it for a different model.

When she got her February bill, she was charged a payment for the new phone and the phone she returned. She figured it was an oversight that Verizon would fix. She paid the total due, though the glitch doubled her usual phone bill to nearly $100.

But her March bill again charged her for two phones. A customer representative confirmed that Verizon had received the returned phone and told her it would take one or two billing cycles to "sort it out." Again, she paid the bill. Troy says she got "a little miffed" when her April bill arrived. "I'm still being charged for both phones!" says the humanities professor at Strayer University who lives in Oakton. Again, she paid the incorrect phone bill.

Ditto May and June.

Troy says she tried calling Verizon but gave up after spending an insufferable 40 minutes waiting to talk to a human on the automated customer service phone system, and started sending e-mails -- more than a dozen -- to Verizon's customer service Web site. She says she never got a response other than automated confirmations. She also mailed five or six letters to Verizon since April and didn't get a reply.

"I explained the same situation over and over again, sent copies of my previous correspondence. Nothing!" she says. "What kind of outfit keeps charging someone for something months after it has been returned? What kind of returns process do they have anyway? One person who types in the information once a month with her toe?"

Verizon spokesman Harry Mitchell looked into the case. "It's apparent that we didn't do what needed to be done to stop the charge for the first phone and properly credit her account," he says, promising that the error has been corrected and Troy will be credited for her overpayments on the bill she receives next week.

"This was purely an isolated occurrence and we're reviewing our procedures to ensure that it doesn't happen again," says Mitchell, explaining that, in billing about 30 million accounts each month, Verizon's overall accuracy is "excellent."

Scott Broetzmann, president of Customer Care Measurement and Consulting, says customer-satisfaction studies conducted by the Alexandria-based research firm in the past year found that the second-most-cited industry in consumer complaints (after automotive) was telecommunications -- the telephone companies.

Billing problems constitute telephone companies' biggest complaints. "About 25 percent of the problems in that industry were billing-related," he says. "Incorrect, fraudulent or deceptive billing was the most frequently cited problem. All kinds of other research speak to the frequency and severity of billing problems in that industry."

But how does a billing mistake like Troy's persist over six months? Speaking generally, without singling out Verizon, Broetzmann says customer relations divisions often use codes for different kinds of problems and unusual billing errors get coded in a way that queues them as "an exception category" and the last to be handled.

"Once you get into the exception category, the speed with which things are handled drops dramatically because all of those exception cases require nonbusiness rules, high-touch care," he says.

Another possibility is that many large companies outsource their customer service, he says. "The communication or lack thereof between the company and the outsource vendor frequently is a source of this kind of problem."

Broetzmann says smaller companies might carry such a payment problem longer than necessary as a cash-flow decision. And employee incompetence, in large companies or small, is always a possibility.

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Got questions? A consumer complaint? A helpful tip? E-mail details to oldenburgd@washpost.com or write Don Oldenburg, The Washington Post, 1150 15th St. NW, Washington, D.C. 20071.