BILLING FOR ITEMS ON A PACKAGE

we have had an adt alarm installed last year Novmeber'14 paid well over 12k for this system. Had all the bells and whistles added including a lock box for them to get into our property when the alarm goes off. We had issues from the 1st week of the installation with the one door contact not making contact all the time. The entire winter this was find now that the rain has started this is starting to act up again. After a couple of times calling to the Call centre regarding an amount they say we have outstanding i have picked up they are charging us for the lock box over the 12k we already paid (Cash) they keep on sending me a sms to say i have an amount outstanding and when i phone no body can help me. now i phoned to get someone to come and fix the system that is still under warrenty and they refuse to assist because im 120 days outstanding with the amount of R380.00 for the lock box that was provided as part of the package. GETTING FED UP BY ALWAYS ASKING WHY THIS ISNT CLEARED..... I WANT SOMEONE WHO IS ABLE TO FIX THIS TO PHONE ME