What does it mean when someone says "i didn't say that i didn't"

It means they did whatever they said they didn't do..

It means that you assumed someone didn't do something cause they never said they did. But when you found out they did do it they say I didn't say I didn't you just assumed I didn't.

Or they could be just really messing with you and want you to think they did do it, just because your annoying them so much! But in reality they never did it