ADT Contract signed, yet so service

I contacted ADT to take over the contract of a house we bought. They came out surprisingly fast, and not only one sales person, they double booked me and I had two sales people with me and hour after each other. My details changed First debit order went off with no problem. Yet while signing I informed both sales personnel that there Is a problem with the one sensor and it does not work properly (I found out it wasn't even connected) however I was told a technician will come out to fix the problem. it is two months later and still nothing happened. on Monday someone tried to break in to the house via the door where the sensor isn't working.... luckily we could press the panic button. ADT only called after the 4th time of pressing the panic button about 20 min later on the secondary number (not the main cell number) this after the alarm has tripped a couple of times in the past two weeks, with no call and no response (PATHETIC to pay for a service you don't get) Anyway, I now called yesterday and was told to get the sensor fixed I have to pay a service fee of over R500 as it is not ADT's fault and I am liable and they don't show to the appointment.. Horrible service. I'm cancelling