The three-piece vocal group, who were placed in the bottom two after coming last in the Flash Vote, lost their place in the competition when the Judges chose to save Hannah Barrett.
The group's mentor Gary Barlow voted to keep Miss Dynamix in the competition after their rendition of Swedish House Mafia's 'Don't You Worry Child'.
But Nicole Scherzinger and Sharon Osbourne voted for Hannah to stay despite the singer fighting back tears during her performance of Emeli Sandé's 'Read All About It'.
Louis Walsh's vote was not needed as Miss Dynamix had already been eliminated, but he said after that he would have also voted for Hannah to stay.
Following the show, X Factor boss Simon took to Twitter to express his disagreement with the decision.
He wrote: "I would have kept Miss Dynamix. I don't get that decision."
Simon left the X Factor judging panel in 2010 to concentrate on the US version of the programme.
Meanwhile speaking after Sunday's results show, Miss Dynamix vowed to remain together as a group.
Band member Jeanette said: "We have a connection, we're friends - we will be staying together as a group."
"To Gary, we say thank you for believing in us - for giving us a chance," added SeSe.
"We feel satisfied and relieved that we showed everybody we could sing. We are gutted - this is how we should have been from the start."
Mentor Gary said he hoped the girls won't give up on their dream as he felt they have a lot of potential.
"They're into the Final 12 of The X Factor, which is surely a sign they're a good group," he said.
"I'd say they need to stick together and keep exploring this idea."
The X Factor returns to UTV for a Disco themed show on Saturday and Sunday from 8pm.