How do I get out of a contract?

In September I signed a contract with a home security co. Since signing system has yet to function as promised. Motion sensors which installed and supposed to be immune to pets under 80 lbs keeps getting tripped by my two dogs which are 50 lbs each. I know have to keep my dogs locked in the basement when the system is armed. The motion sensors sometimes don''t go off when a person enters the room. Police have been to my home several times due to the alarm being triggered for no apparent reason. They installed the main panel where all the security is tied into and the signal goes to the monitoring station, in my basement with next to an unprotected window. When I complained they installed a window contact and are trying to charge me for it. I emailed a cancellation notice to them at their request was given an appointment to remove equipment, then was told they needed to cancel the appointment, it was a liability for them to come out and remove equipment.