Question: In the last one week, we have been receiving calls from a number. As soon as the call is attended, the caller disconnects. We receive more than 10 calls from this number every day. How do we BLOCK calls from this number?

Answer: You will need the "App builder" for this. 

Create an empty list called "Blocked Callers":

Create an app called "Call blocker": 

Use the "Who's calling" Applet and choose "Blocked callers" as the list. 

Now, ask exotel to "hangup" calls if the caller belongs to the "Blocked Callers" list. Else, "Transfer" the call to your usual flow. 

Now, As and when you find prank callers - Add their number to the "Blocked Caller" list from your address book page.