Sentence examples for ain't so from inspiring English sources

The phrase "ain't so" is correct and usable in written English, though it is informal and often considered colloquial.
You can use it in casual conversations or informal writing to express disbelief or contradiction regarding a statement.
Example: "I heard you think the movie was boring, but that ain't so; it was actually quite thrilling!"
Alternatives: "isn't true" or "is not the case".