For a start, there is a logical error here. Just because not all religions are true, it does not follow that they all are false!
Another fallacy is that the number of religions is greatly exaggerated. I have seen references to "thousands" of different religions more than once. The essential different ideas of God are really very few:
Of course there are thousands of proposed ways of following and worshipping God. But these all revolve around the same few "Gods". And many of these ways are not mutually exclusive (for instance the differences between Christian denominations are dwarfed by the similarities).
Another reason why the proliferation of religions is not a problem for the Christian, is that it is actually the situation which the Bible explains and predicts.
The Bible offers two reasons why people do not all follow the true God. First, people are naturally rebellious (theologically, the term is "The Depravity of Humanity"). We all have a natural inclination to not follow God's ways. Secondly, the Bible says that people are actively misled and deceived by the Devil. Furthermore, the Bible says that this will continue to happen, even within the church. So while the proliferation of religions, and splits even within the Christian church, are a sad state of affairs, the realistic Christian will realise that that is a natural outcome of the sorry state the world is in.