Cancelled in 2013

We cancelled our agreement with ADT end of 2013 and paid the outstanding balance in January 2014. Since then we have periodically received sms's, phone calls and emails to say we have money outstanding. They have forward copies of the invoices which they say are outstanding but according to my records those invoices were paid. I have emailed them a copy of the payment proof as requested to every different email address that they have provided and asked for them to confirm they received the documents but they never respond and still keep threatening to list us for non payment! It is beyond ridiculous and we are so glad we decided to move to another security company.