Marvel not when the unbeliever denies your claim of inner transformation and life in Christ. They are dead and are wholly unable to know the life that is in Christ, which is given only to those who place their faith (belief & trust) in Him as Savior.
It should be no more surprising that unbelievers should deny every spiritual experience of the Christian than it should surprise you that a corpse ignores those attending a funeral.
Knowing this should spur us on not in arguments or debates with unbelievers but rather in proclaiming the Gospel to them. Through the Gospel, the Lord may grant them faith; only then will they stand upon the same ground as we believers do, and being awakened to spiritual life, they are now free and able to come to an understanding about what is spiritual.
There’s a reason the Scriptures tell us to rebuke heretics only twice; to continue to land blows upon the dead just makes you look silly, and in my experience, it gets messy quick. Besides, surely you have better things to do?