To check whether your contacts block you, you
may refer to the call and messages status.
(1) Your buddy is not online
If the call failure shows "your buddy is not online"
and the messages you send to them show only one
check, it means the messages have been sent out,
but they haven't received your messages.
It may be caused by network delay or they are
offline now.
(2) Another reason is that they blocked you.
When your messages sent out keep showing
only one check, then you can assume that they
probably blocked you.
They won't receive your messages unless they
unblock you from the blocked list.
Note:
The notice of being blocked is now changed to
'Can't call this user due to his/her privacy setting'.