bobbyachitei said:

Is it possible to unblock a player? How can I do it?

http://prntscr.com/dkbsho

click on Blacklist on your message box and remove them from there

moved to game discussion 

yes you can unblock players either from chat or reports mail .

all you have to do is what lord jez said http://prntscr.com/dkcx02

click undo next to the player :)))