How do you say 'didn't I tell you' in Japanese?

君に言うことはない。(kimi ni iu koto WA nai.)

Improvement:

The sentence above would translate to 'I don't have anything to tell you' (言う事 : 'iukoto' can also mean 'advice'). A bit more precise sentence for this question would be 'anata ni iwanai (anata ni iimasen -> more ploite).