In order to block a number from calling you, all you need to do is to click "Mark Caller as SPAM" as soon as you finalize the call.
The system will then ask you if you want to mark the caller as a SPAM
By pressing "Mark as SPAM" you will add the number to your SPAM List, this way preventing the number from reaching you again.
You can easily view and modify your SPAM List by heading over to Admin -> Spam Numbers. This page gives you the option to manually add a number to your Spam List or to delete an existing one.
Feel free to ping us in case you have further queries.