TORONTO – AlarmForce Industries Inc. says some of its customers were incorrectly billed over a three-year period, resulting in a delay of its next financial report.

The Toronto-based company said in a statement it shouldn’t have continued charging monitoring fees to customers in some jurisdictions after they cancelled their subscriptions but before they returned AlarmForce’s equipment.

The home security firm said it discovered the problem after conducting a review of its residential subscription cancellation practice while carrying out due diligence for a potential sale of the company.

AlarmForce (TSX:AF) did not disclose in its statement how many customers were affected, nor how much money was involved, but it says it will contact those subscribers over several weeks beginning Aug. 29 and is promising refunds.

It is reviewing residential contracts starting as early as Aug. 1, 2013, a process it said will delay completion of its fourth-quarter financial report past the Sept. 14 deadline.

AlarmForce provides security alarm monitoring, video surveillance and other related services to homes and businesses throughout Canada and the U.S.