言ったことがわかりません, the romanization for this phrase is "itta koto ga wakarimasen" the subject of the phrase is implicit.

The translation is: あなたの言[い]ったことがわかりません or 理解[りかい]できません。 *We use (name)さん very often instead of あなた However, I would say: よくわからなかったので、もういちどおねがいします。(=Since I didn't/don't understand well, please say it again / once more, please / please repeat it.) I hope this helps you.