Praise be to Allah.
Shaykh ‘Abd al-Rahmaan al-Barraak answered this question as follows:
“Those who never hear the call of Islam, or they hear about it in an incorrect form, will be tested on the Day of Resurrection. Whoever obeys will enter Paradise and whoever disobeys will enter Hell, because Allaah says (interpretation of the meaning): ‘… And We never punish until We have sent a Messenger (to give warning)’ [al-Isra 17:15].”
And Allaah knows best.