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Rampage Jackson is picking a fight with the UFC ... claiming he'll NEVER fight for Dana White ever again because he feels the organization has treated him like a chump. But Dana says Rampage doesn't have a choice ... because the UFC doesn't WANT him back.

Rampage was leaving AV Nightclub in L.A. Monday night when we asked about reports that he was retiring from the sport ... in the wake of Saturday's loss to UFC fighter Glover Teixeira.

"I didn't retire from MMA, " Rampage said ... adding, "But as of now ... I've left the UFC."

He continued ... "The UFC didn't treat me right. I don't like the way I was treated there."

So what pissed him off? Rampage says he was screwed out of cash ... and he feels betrayed over a deal involving Rampage action figures.

Jackson says he's hungry to sign a new deal with a rival MMA company so he can forget the UFC for good -- but he's contractually obligated to wait a month after his last fight until he can sign a new deal.

We spoke to White -- who couldn't have been more direct ... saying, "Rampage didn't quit. He lost his last 3 fights and his contract is up. Do you see me beating his door down to get him back?"

White continued, "From 2007 to 2012, Rampage has made $15.2 million with the UFC. Ask him how much he made from the 'A-Team' when I let him go film it."