Paris Jackson -- Instagram Account Isn't Me ... Shut It Down

Paris Jackson is adamant, the Instagram account posing as her that changed its last name to Jackson Castellaw isn't the real deal ... and she wants it shut down.

In a video posted to her bf Chester Castellaw's alleged page, Paris asks fans to help her get the impostor account -- which has racked up more than 200k followers -- removed. She claims she does not have a public profile.

It's interesting ... the video doesn't address marriage rumors but a source close to Paris says the two aren't married.

As TMZ reported ... fans began to buzz about Paris and her 18-year-old bf tying the knot after his last name was added to an IG account claiming to be her.