100% Surety Of Life After Death?
First, you need to know the truth of the religion and then you believe in the news and information provided by religion about the metaphysical world. It is only NEWS that has to be believed in. How do we come to believe that the message of God that is Islam really came from Him? this is the question you need to deal with. For that, kindly watch the Zawiya series of Ghamidi saheb and his other talks in which tells how Islam is established to be the word of God.
A series on atheism is going to start soon, keep an eye on it. You can search with the keywords like atheism, Qurna the word of God etc to search Ghamidi Saheb’s talk on these issues.