If you need to block a contact:
Enter the app within the Chat menu that you will find in the second tab of the menu in the lower area.
Go to the top right of the main screen you will see the icon of an address book📔.
With the help of the magnifying glass 🔍 search for the contact you want to block.
Select the contact and at the bottom select: Block contact.
When you block a contact they will no longer be able to send you messages.
How to unblock a contact
If you change your mind it is possible to unblock a contact. To do so:
Enter the app in the Chat menu that you will find in the second tab of the menu in the lower area.
Go to the top right of the main screen you will see the icon of an agenda📔.
With the help of the magnifying glass 🔍 look for the contact you want to unblock.
Select the contact and at the bottom select: Unblock contact.
If you have a conversation with that user you can also unblock them directly from there.