Learn English – must not have done vs might not have done

grammargrammaticality

Q) It was very kind of you to do the washing up, but you — it

Should it be "did not have to do" or "might not have done" or "must not have done"?

They all seem to convey same meaning in general to me. Which is correct grammatically?

It was very kind of you to do the washing up, but you did not have to do it.

converts to

Your action was not necessary.

To have to is to be obliged to¹.

It was very kind of you to do the washing up, but you might not have done it.

converts to

It is possible that you didn't do it.

Might is "used in auxiliary function to express permission, liberty, probability, possibility in the past"²

It was very kind of you to do the washing up, but you must not have done it.

converts to

I have come to the conclusion that you didn't do it.

Must is "used to indicate logical probability or presumptive certainty"³