But I didn't! có … đâu, đâu có

You know không … đâu, which makes a "no" firmer. Có … đâu goes further: it denies something someone has said or assumed, like "But I didn't!" Put có before the verb and đâu at the end, with no không: Anh có biết đâu. I had no idea (so don't blame me).

In Saigon the most common form puts đâu có before the verb: Em đâu có nói vậy! I never said that! (in Hà Nội, nói thế). It works before describing words too: Đâu có mắc! It isn't expensive at all! On its own, Đâu có! means "No, not at all!" or "That's not true!", a very common reply. In quick speech đâu alone can do the job: Em đâu biết! How would I know?

With a noun, add phải, as you would after không: Em có phải con nít đâu! I'm not a kid! Đâu phải works the same way.

These sentences push back, so they can sound defensive. With someone older, start with dạ to keep it polite: Dạ, đâu có! For a calm, neutral "no", plain không is enough.