Billing after service was cancelled

My wife sold her car in december 2013 and cancelled her tracker device in that car.. But till today they are still trying to debit her account. She has twice told them over the phone to cancel it and per email but tracker say they dont have record of this. Now my wife who is on dissability after a stroke some 8 years ago is listed on itc. All this because of R646... If they just stopped it when she asked them to thats all we wanted. Its been a masive strugle and we will never put a device from Tracker in any of our cars again