Many block development officers from South and East Garo Hills and businessmen in West Garo Hills have received the notes.
The outfit, formed by the former deputy superintendent of police, Champion Sangma, two years ago, is active in all the three districts of Garo hills and West Khasi Hills.
West Garo Hills superintendent of police Dalton Marak told The Telegraph that the numbers were found to belong to fictitious people.
Some extortion messages are believed to be sent by the outfit’s self-styled finance secretary Jakpil Sangma, who used fake identity cards to procure the cell phones.
Marak said the militants mostly use mobile phones of private telecom companies. “We tried to track some messages, but the militants either switch off the mobiles or make them unreachable,” a police official from East Garo Hills said.
Marak said four persons were caught in Tura in May while distributing SIM cards in West Garo Hills. He said the racket had spread to Manipur and Nagaland.
The police came to know about the racket after the arrest of the outfit’s general secretary, Novembirth Marak, in May. Marak confessed that some agents of the mobile companies had procured registered pre-paid SIM cards from Nagaland and Manipur.
“We want the mobile companies to see that the SIM cards are issued after proper verification,” the SP said.