That's sad news, but I saw it coming all along, watching the ratings season 3 gets so far :'(.
Well, at least NBC will air the entire season and not drop it now. And, honestly, I cannot blame the network. NBC let this show survive on horrible ratings for the past two seasons, they had tons of ads for Hannibal. It's not their fault, its the audience, sadly but true.
So sorry to see this little gem go ...SpoilerTV