50 Cent Claims Song Theft Accuser Doesn't Even Own Song

As TMZ first reported, a man named Robert Poindexter sued 50 ... claiming the rapper hijacked a sample of his Persuaders song "Love Gonna Pack Up and Walk Out." Robert claims 50 used it on his track "Redrum," which he released for free online.

But in recently filed court docs, 50 says the suit is bogus and claims he never violated any copyright laws. In fact, he says Robert doesn't even own the rights to the allegedly-stolen song because he signed them over to Warner Music Group awhile ago ... therefore he can't sue.