Poor service by Blue security

Blue security breached our contract first in January beginning of this year by not rendering the service that we agreed on, when I wrote a cancelation letter almost a month later, they were telling me to continue paying for the contract, for the services that am not getting from them based on the breaching of contract that they broke first so I told them I won't pay that amount of money, they should take me to court if they want to but I cant pay for the services am not receiving mainly bcos I was not happy and frustrated bcos they could not render their service at all while I was away from home for weekend. So now they continue billing me till now and have just started yesterday t harass me with phone calls. Am terribly hurt by their desperate unprofessional behavior towards me after they failed to deliver till I decided to go for another company just for my own peace of mind