For Maureen Coffin of Stoneham, Mass., it started on July 21 — the insistent calls from debt collectors demanding she pay $900. For what, they never said. Since May, Deborah A. Donovan of Weymouth has received at least 25 calls — many of them abusive, she says — and two letters asking her to pay $4,900 for a delinquent Sears credit card.

Eileen R. Myers of Harvard had a longer nightmare — 18 months of annoying phone calls and letters from five successive debt collection companies insisting that she pay a delinquent Capital One credit card bill.

In all three cases — and thousands like them, specialists say — the posse is chasing the innocent. Maureen Coffin was being asked to pay for a debt owed by a Lorraine Coffin. Donovan's tormentors, it turns out, only discovered last week that the Sears cardholder is Deborah Doyle — not Donovan. Capital One Financial Corp., one of the country's largest credit card issuers, hired debt collection firms to go after Eileen R. Myers. The name of the actual debtor: Eileen A. Myers.

Debt collection, as the Globe Spotlight Team reported in a recent series, is a major growth industry: Tens of millions of consumers are being pursued by armies of collection agents and lawyers for hundreds of billions in delinquent debt, much of it sold and resold to one debt collector after another. The debtors are, the series found, often subject to exorbitant fees and roughhouse treatment, even in courtrooms where judges and clerks frequently favor debt collection lawyers.

But there is parallel phenomenon, with its own unchecked growth: cases of mistaken identity, in which the abused consumer owes nothing at all.

After the Spotlight series, hundreds of people called or e-mailed the Globe to complain about debt collectors. Many said they had been pursued for debts owed by others with identical or similar names; or asked to pay debts for ill or deceased relatives; or besieged by debt collectors for the misfortune of having phone numbers once held by people who defaulted on their debts.

In some cases, the mistakes border on cruelty. In October 2003, Marjorie and Allan Slotnick of Brockton received a demand from a debt collector that they pay a 1995 Southwestern Bell phone bill, for $484, purportedly owed by their son. But Adam Slotnick was killed in the Northridge, Calif., earthquake in January 1994 — a year before the debt was incurred. The Slotnicks sent the debt collector a copy of their son's death certificate, thinking that would be the end of it.