Being changed for services that weren’t offered

I am shocked by the harassment to pay from ADT security company in Herm****, in 2012/2013, I made an application to change the home alarm system to adt and a technician was sent out. He came twice checked the system that was in operation then and said , the was a lot that needed to be done and he would come back again, we were never told that the alarm was activated as we didn’t even receive remotes and no codes were activated. Now to my surprise ADT claims we owe them, what do I owe them for ? When no alarm was ever put in? Worse they are threatening to blacklist me. Is this some kind of a money making scheme? Please assist