WhatsApp has listed a few ways in which you can tell whether your number has been blocked by a specific person/contact. However, there's no way to be 100% sure
WhatsApp provides the functionality of blocking people in their chats to stop getting new messages from that contact. However, the person who is blocked does not get any notification of the same. WhatsApp has listed a few ways in which you can tell whether your number has been blocked by a specific person/contact.
Here are a few ways to know that you’ve been blocked:
You can no longer see a contact's last seen or online in the chat window
You do not see updates to a contact's profile photo.
Any messages sent to a contact who has blocked you will always show one check mark and never show a second check mark
Any calls you attempt to place will not go through.
If you see all of the indicators above for a contact, this could mean that the user is blocking you.
Despite the above-mentioned pointers, there is no way to be 100% sure that the contact has blocked you or is dealing with a connectivity issue. According to WhatsApp, they have made this intentionally ambiguous in order to protect the user's privacy when they block someone. WhatsApp will never relay the information directly to a contact that they are blocked.
Apart from just blocking contacts, users can even report them if they think they are sending problematic content or spam.
How to block a user on Android
Open WhatsApp, tap More options icon (three dots) and then Settings.
Within settings Tap Account > Privacy > Blocked contacts.
Then tap Add.
Search for or select the contact you want to block.