he is probably a hacker
blocking doesn't work?

he is probably a hacker
if anything doesn't work >>>> assume someone is a hacker.

he is probably a hacker
Or you could think logically
who would want to do that

No, if you join a game queue that they are already in and then block them. Make sure you block them before you join a new game. Its happened to me before.
update: after blocking the same person, 2 games later, that person is my teammate. I resign, lose a point and can't join the queue where that person is (last game, that person joined after me). So it is possible to get the blocked person as your teammate

blocking doesn't work in any anonymous games, even if the blocked person is your teammate. I suggest not playing anonymous for teams, or even semianonymous.
it happend to one of my friends, who blocked a person after being a partner with them in a game. Then both of those guys were partners again, while the one was blocked. The reason could be the fact, that it was anonymus game, but why didn't it work? If I block somene, then that someone is blocked???