Never receive Statements or Invoices

I rent from Remax a home in Westering for my Children. ADT Security is the service provider for the alarm and security. My Children have lived there for 2 yrs now and each month I have to request a statement and invoices. I never receive them. Finally I received a notice of outstanding amounts due. I did not realise that there had been an increase! To date I have still not received an invoice. Recently I wrote a letter to Carla explaining that my children would be vacating the property in Westering in February 2016 and this then is my letter of notice and my last payment to ADT will be February 2016. I requested a acknowledgement in receipt of this letter. That was in November 2015. It is now January 2016. Still No Response. Now What?