Learn your religion well, address their clear falsehood in their religion and how corrupt it is and turn the table on their heads. Attack their corrupt bible that has thousands of contradicting versions while Quran is the same since over 14 centuries, not changed and in the same spoken language used today.

As we encounter christians missionary in our life time, they get knowledge of Islam and on that basis they raises question regarding Quran and even Hadiths. They show some ahadith which seem like contradicting the Quraan and some seems like it is not from Prophet Muhammad PBUH. So how to tackle them in that cases.