There are a couple of indicators that you may be 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 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.
If you see all of the above indicators for a contact, this could mean that the person is blocking you. However, there are other possibilities. We have made this intentionally ambiguous in order to protect your privacy when you block someone. Thus, we cannot tell you if you are being blocked by someone else.
Not sure what blocking someone does? More details Below
Blocking someone will not remove this contact from your U Chat Messenger list, nor will it remove you from the list on this contact's phone. To delete a contact in U Chat Messenger, you must delete the contact from your phone's address book.