ADT refuse to replace 9 year old rented system!

I have been a loyal client for ADT for over 9 years!! Business and home and never even defaulted on a single payment. I have rented alarm systems which belong to ADT. And because my business alarm is over 9 years old, its going abit crazy. Goes off sometimes for no reason at all. I have tried many times to have ADT replace the system as it is old. They refuse. I keep getting charged for extra call outs(u allowed 5 a month, all of a sudden its apparently 3!). Its NOT MY PROBLEM THAT YOUR SYSTEM IS FAULTY. THIS IS MY LAST RESORT, and if i dont get a brand new working full complete system thats the end of our contracts for both my business and home And i WILL CONVINCE family and friends also to move to the more efficient CHUBB. How hard is it to service a client. 9 years!!!!