ADT dont maintain rented alarm systems

Been with ADT for 9 years now. Every 3 years they're supposed to give me a new rental system or maintain mine. They refused to do so. They lie and promise nothing happened. I finally got fed, bought my own system, installed it at my expense. I just called them to link it to their system, they still want to charge me ! They're supposed to give you a new system every 3 years. Utter *******.