We quite often say "You say you are happy, but your face says otherwise" Otherwise has a similar meaning to opposite. In English we would not really say "your face contradicts".

"You say you are happy, but your face says the opposite."

I'd choose "your face contradicts"

Your face tells a different story. Your face says the opposite. "Your face contradicts" is not a complete sentence. You need to say _what_ it contradicts.