That's odd. You say this has happened before... it sounds like the keyboard is faulty if the letters won't type. How old is the 9650? Is it still in warranty? A CPO replacement may solve the problem - I'm using a CPO and it's been just fine.
My first thought was to do a battery pull, but you said you'd already tried that. Is there a game or other program running in the background that maybe uses those keys and has them reassigned? Use the Alt + back arrow key to see all the open, running programs, close any you don't need (there are 5 or 6 that will be open regardless - browser, Home, phone, messenger, messages).