sadly, church history does not seem to be your strong point.
you say the church for the first 400 years had a 66 book bible. really? please provide one canon of scripture during this time period that lists 66 books. i’ll save you time, one doesn’t exist.
the OT used by St Paul contained these books, and they have always been used by the Catholic Church.
some ancient churches broke away from the Catholic Church in the 3rd and 4th centuries, such as the Coptics and Oriental Orthodox. here is a history homework assignment for you, do they have a 66 book canon?
I do agree that Satan attacks Christianity by attacking the Word of God, but also the authority of the Church. Sadly, in the 16th century, by claiming the Bible was wrong and the Church was wrong, he did great damage to Christianity.
Me thinks you need to do some reading. I’m not going to do something you are capable of doing yourself. It’s pretty easy research I’ve already done. You may find the NT was in place before 200 AD. I’ll let you do the rest.