It is nothing new to see these claims and it is part of the ongoing false propaganda against Islam which is going on since over 14 centuries but fortunately with out any success. The facts of Quran are clear for those who have knowledge despite these false allegations. The proper study of Quran proved that there is no contradiction at all for those who understand the meanings away from their own imaginations.
All these claims have been refuted one by one by our scholars who took their knowledge from Ahlul Bayt (AS). There are many books compiled in this subject like Al-Ehtijaj which contains some answers from Ahlul Bayt (AS) on some claims.
Now a days we find many enemies trying to use wrong translation and claim contradiction.
If you need any help in refuting any specific claim or claims, you are welcome to write.