Sinn Fein Councillor Maeve McLaughlin has warned home phone users in NI about a new scam.
The scam involves a call from someone who claims to be from BT demanding payment for an outstanding bill.
Cllr McLaughlin said:"The scammers ask for bank or credit card details and warn that if payment is not made, the line will be immediately cut off."
BT said customers should never give out banking details unless they know exactly who they are dealing with.
To convince bill-payers that they are calling from BT, the scammers pretend to temporarily disconnect the phone.
When the victim hangs up and tries to ring out again, there is no dial tone and the phone line is apparently dead. The fraudster then rings back to get the victim to hand over their bank details.
BT said that while it does sometimes call customers to recover debts, it never carries out disconnections during the call.
Ofcom, who also issued a warning about the scam, said that BT employees should be able to give customers an employee ID number and a freephone number to call to check they are genuine.