In the Department inbox, click on the call with the number you want to block

On the conversation screen that opens, on the right side under "Profile", there is a Block Contact option. Click on it.

Alternatively, there is now a banner that shows up across the top of the conversation screen, with a "Block or mark as spam" option. You can click that one also.

A pop-up window will open, giving you 2 options for blocking calls & messages from this specific number.

Option 1 - sends all calls to voicemail

Option 2 - plays the caller a message that the number is no longer in service, then disconnects

Select the option you want, then click on Block.