If you want to prevent a person from calling inbound to your office, use the Blacklist module. The first step is to determine the exact Caller ID of the person calling.
To find this, navigate to Reports > CDR Reports. In the extra options, change the result limit to 1000 and hit search at the bottom.
This will display the last 1000 call results, inbound and outbound. Find the the number you want to blacklist. In the example below, you can see an inbound call from 17167515500. Copy the text between the <> signs.
Next, navigate to Admin > Blacklist and click Blacklist number.
This will open the window to add a new record. The number/Caller ID is required, and the description is optional. After filling out fields, click "Save." This number will now be blocked from calling in.
Additional Blocking Features
Go to the settings tab in the blacklist module.
Block Unknown/Blocked Caller ID: This will prevent inbound calls that show up as non-standard blocked Caller ID.
Destination for Blacklisted calls: The default is a system hang up, but you can select a different destination.
If you change additional settings, you will need to "Submit" at the bottom of the page and "Apply Config" at the top. This step is not required if you are only adding a new record to the Blacklist.
This module will only block calls that match exactly to the data in Number/CallerID.