All Church cannot be right. There is either one correct or none of them are.
As for the Bible, it's a good tool to bring men closer to God, but it can only do so much. That's why the Lord gave us the Holy Spirit. So we aren't fending for ourselves but learning straight from Him.
Satan doesn't decieve people by telling them outright lies. He decieves them by mixing some of the truth in his lies and convincing them that because one principle he is teaching is correct they all are. The Bible is useless without the Holy Spirit. God is the final authority of all truth, not the Bible. The Bible leads us to God. It is in God we are to trust, not the flesh. We can't tell God "I'll only believe what you said in the Bible, but anything else and I won't". We are supposed to live off every Word that proceeds from the mouth of God. Whether he says it 2000 years ago, today or whether He says it in the future. And God hasn't stopped speaking.
Does God still speak? if you limit what He says to that which has already been said then no He doesn't. And that would be a changing God, because the Scriptures teach of a God who communicates regularly and commands them to testify of their experiences.