There are a few indicators to know whether someone has blocked you on Whatsapp:
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 picture.
Any messages sent to a contact who has blocked you will always show one check mark (message sent), and never show a second check mark (message delivered).
Any calls you attempt to place will not go through.
Try adding the contact to a group. This testing will not leave doubts: if you want to know if a contact blocked you try to add a group conversation. If you see a message that appears to do: “You are not authorized to add this contact,” sorry … Indeed, it has blocked you.
Try adding it from another phone. Another infallible test is to ask a friend his/her phone, or occupy another alternative you have, and add the contact number that you suspect has blocked you. If you can see a picture of a different profile or other status message, it is virtually certain that you have been blocked.