Alipurduar, Feb. 27: Hoax calls made by three teenagers had forced the railways to stop Kanchankanya Express twice to run a check on the tracks in north Bengal last night.

The Class XI students of McWilliam High School here made the calls from a cellphone between 7 and 8pm, while returning home from a private tuition. The phone belonged to a guardian of one of them. They took advantage of an offer of unlimited free calls given by the service provider of the cellphone. Yesterday was the last day of the offer.

The boys had made 22 random calls in one hour — most of them to Calcutta. They threatened someone with exploding a bomb in his house, while frightened another with a robbery bid.

The callers also rang up the personal assistant of Sobhandeb Chattopadhyay, the chief whip in the Bengal Assembly, and identified themselves as extremists from Jharkhand. They told him that the Sealdah-bound Kanchankanya Express would meet with an accident before reaching Malda Town as fishplates on the tracks had been removed, the police said.

Chattopadhyay’s aide immediately contacted the Calcutta police control room in Lalbazar and the call was traced.

The train was stopped at New Jalpaiguri station for 20 minutes at 8pm and again detained for 15 minutes before reaching Malda around 12.30am. After the tracks were checked thoroughly, the Sealdah-bound train left for the destination.

After senior officials from Calcutta contacted the Jalpaiguri district police, the inspector-in-charge of the Alipurduar police station, Sitanath Das, picked up the boys and their guardians for interrogation.

“We grilled the boys for three hours and believe that they had committed the nuisance unintentionally. We have cautioned them against doing this in future. They also signed an undertaking. The callers were released considering their age,” Das said.

Sudhangshu Biswas, the headmaster of the school, today said he would no longer allow any student to carry cellphones on the campus. “Whatever the students have done are very unfortunate. All the three are meritorious and have secured over 700 marks in Madhyamik Examination,” he said.

The headmaster said: “Soon we will convene a guardians’ meet to request them not to allow their wards to use cellphones in schools.”