Beyonce -- 7-Eleven Claims Slurpee Pic Was All Her Idea

Beyonce was not in cahoots with 7-Eleven when she made her new "7/11" video ... so says 7-Eleven.

According to a spokesman for the convenience store giant ... the Slurpee pic she posted on Instagram to promote the vid has the Internet going crazy ... but that was simply Beyonce going rogue, and NOT a marketing ploy for 7-Eleven.

Of course, that's not keeping 7-Eleven from reveling in the afterglow, telling TMZ ... it's clear why she chose their frosty beverage, "because a Slurpee is the coolest drink on Earth."

Brain freeze in 3 ... 2 ... 1 ...