Usyk went down gasping for breath after being hit on the band of his shorts in the fifth round. The referee ruled it a low blow and told Usyk to take his time as he remained on the canvas grimacing, with the round eventually continuing.
Usyk then finished the fight in the ninth round to retain his WBA, IBF and WBO belts.
"I should be a world champion right now," Dubois told the BBC, calling for a rematch.
"It wasn't justice. It needs to be called out and go further than living this lie. They just cheated out there."
Dubois said the body shot was something they had worked on in training.
"It wasn't a low blow. I felt it land perfectly," he said.
"We've been working in the gym for weeks and weeks on end on that shot. We pulled it off and that should have been our moment. That should have been a knockout."
Dubois' promoter Frank Warren said after the fight that the referee "got it badly wrong" and his team would take action seeking either a no-contest or rematch.
Usyk's promoter Alexander Krassyuk said he saw "several low blows" from Dubois during the fight.
"Everyone wants the rematch after he loses a fight," Krassyuk said in the post-fight press conference.
"Sometimes it happens, you hit someone with an illegal blow, yeah it is normal. But when you keep doing this on purpose, it means you have some sort of dirty plan ... We saw several low blows."
When asked about a rematch, Usyk told reporters: "I'm ready for a rematch tomorrow in a street fight."
