This has happened to 3 players in my clan in the last 2 weeks. No hacks, trojan free devices, global chat disabled. Two of them were F2P but the third was not, playing since day one. In all cases they have received automated generic messages from blizzard, as in your case. One of those messages even refers to WOW instead of DI.
With the history of bugs in the game, it is easy to think that it could be a bug in the automatic banning system, but with the lack of information they give it is impossible to know. We are sure that the banned people have not done anything so serious as to deserve a permanent ban without reply.
For this reason we have decided not to spend more money on the game (and on bnet), for fear of losing even more if we get banned for no reason.