Mary Kate Cornett Parents Say They Felt 'Helpless' Amid Internet Hoax

Mary Kate Cornett and her parents are coming off an emotional 48 hours ... one which her parents said left them feeling helpless -- though a recent development may help the Cornetts take some of their power back.

We spoke with Mary Kate Cornett's mother, Leslie, and her father, Justin ... who tell us all the claims about their daughter floating around on the internet are untrue.

We're told the last couple days have been difficult for the trio, who are all spending time together in Oxford, Mississippi -- the city where the University of Mississippi resides.

As you know, Cornett -- an 18-year-old freshman at Ole Miss -- has been dragged on the internet for allegedly sleeping with her boyfriend's father ... which resulted in her being treated "like she wasn't a human being" online, according to Leslie.

Justin says he and Leslie flew from Houston to be with their daughter when this story started taking off ... but, despite being with Mary Kate to keep her safe, he says "we felt absolutely helpless."

However, the family seems to be fighting back now ... 'cause TMZ has obtained a copy of the police report they filed -- claiming Cornett's been the victim of cyberstalking and harassment.

The police report lays out a narrative ... in which Cornett claims she found out about the viral rumor while at a salon in the area -- and, she immediately raced over to her boyfriend, Evan Solis' house to assure him the rumors weren't true.

Mary Kate and Evan have both denied all these claims on their Instagram accounts ... with Mary even calling out several prominent sports figures like Antonio Brown and Pat McAfee for fueling the unsubstantiated rumor.