As far as I know he wasn’t accused of using the ‘n’ word was he? He was accused of calling Ferdinand a “black ‘c’ word”. That was caught on tape, and he admitted he’d said it.
His defence was, that, during the match, Ferdinand had accused Terry of calling him a “black ‘c’ word”, and Terry was saying something to the effect of “No I didn’t call you a …” when he was caught on film. Cole seems to have partially backed him up on this sequence of events.
One man’s word against another, no proof either way, so he simply cannot be convicted.