Search for or select the contact you want to block.
Here are a couple alternative options for blocking a contact:
Open a chat with the contact, then tap More options > More > Block > BLOCK or REPORT AND BLOCK, which will report and block the number.
Open a chat with the contact, then tap the name of the contact > Block > BLOCK.
Block an unknown phone number
Open the WhatsApp chat with the unknown phone number.
Tap BLOCK or REPORT AND BLOCK, which will report and block the number.
Blocked contacts will no longer be able to call you or send you messages.
Your last seen, online, status updates, and any changes made to your profile photo will no longer be visible to contacts you've blocked.
Blocking a contact won't remove them from your contacts list, nor will it remove you from the list on the contact's phone. To delete a contact, you must delete the contact from your phone's address book.
If you're concerned about whether a blocked contact will know you're blocking them, please read this article.