React Alarms poor service from their Accounts Dept

React alarms installed several cameras at my business about 6 months ago. Their technician was unable to connect the system to our pc and my laptop. He said the windows system was too old. I contacted my IT guy who confirmed my windows was not too old and successfully connected the cameras to the pc and laptop at a cost of R531.00. I then contacted React Alarms accounts dept and told them i would be deducting this amount from my final bill. Six months later after sending about a dozen emails and several phone calls I am still getting letters from them saying I am going to be blacklisted and the usual threats. I have tried everything in my power to reach out to them to credit my account to no avail. They don't even reply to my emails. I am very disappointed as I wanted to install more cameras but definitely wont be doing it through React Alarms.