Charging for a service that wasn't delivered

My blue security system was installed at the beginning of June and has not worked for even a day since installation. Technicians have come back to check the system with no success of fixing it. I have made numerous calls to report this and have made the accounts, sales and technical department aware that the alarm is not working. However, they have still sent me an invoice charging me for the month of June! Why must I pay for a service that I didn't receive? I have wasted lots of time waiting around for technicians and speaking to every department with no assistance.<br> My advice... Don't waste your time with blue security.