Soulja Boy -- Sorry, I Ain't Your Baby Daddy

Soulja Boy has consistently claimed he did NOT father a son 7 years ago ... and now he has the paperwork to prove it.

The rapper's ex-GF Diamond Shantaniece Mackey had claimed Soulja was her son's biological dad, but he denied it. Last year Mackey unearthered a 2007 photo of herself and Soulja in a bedroom -- the year her son was conceived -- so he finally agreed to take a paternity test.

TMZ obtained a copy of the results ... which show Soulja is NOT the father. Sorry, Maury fans.

Soulja's rep Miami Mike tells us he's pissed Mackey's been calling him a deadbeat dad. He also feels bad for the kid who still doesn't know his father.