According to Kolkata Police, at least 450-500 cases of such fraud are reported daily from different police stations in the city.
Investigations into the racket have led Kolkata Police sleuths to Jharkhand, which has become the "headquarters" of such frauds, a police officer said.
"Since last year when the first case of such debit card fraud was reported in the city, it has gone up by leaps and bounds. Now we are getting around 450 to 500 cases every day," said Soumya Banerjee, officer-in-charge of anti-bank fraud section of Kolkata Police's detective department, said.
There are innumerable rackets operating from Karmatar in Jamtara district and Madhupur in Deoghar district in Jharkhand, the officer said.
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There are areas along West Bengal-Jharkhand border near Asansol where families have flourished by duping victims across India, he alleged.
The first case of such fraud over phone in the city was reported in July 2014 when a 30-year-old Belighata resident had received a text message from an unknown number that his debit card has been blocked. Few minutes later he received a call from a person claiming to be a 'customer care executive' of his bank to help him 're-activate' the debit card.