I have been watching a film today named "The Invisible Man", year 1984. And in the second episode i have listened next: "I said... don't touch nothing". It isn't grammatically correctly, is it?
People say that.
We might get taught in schools not to say it. But to some people it's the natural way to talk. It's not ungrammatical to them.
It would probably be ungrammatical on a test of so-called standard English. But who decides what is standard? The test makers and those with socioeconomic power.