First off, thank you for adopting from a shelter.
Was the shelter able to give you any history on Ozzie?
Are you boxes covered or uncovered? Is there a scent to the kitty litter (I am not familiar with the brands you are using)? If they are all covered, try an uncovered. How big is Ozzie compared to the box, he may prefer a shallow, larger in area, than a deep one that maybe to small for him to move around in. If there is a scent, try an unscented one.
Have you changed the cardboard and used an enzyme cleaner to get out residual smells on the floor and sides of the litter boxes that you may not be able to smell, but he does?
I also meant to add, that kitties don't have the same emotions as humans. They are not defiant, or seek revenge as humans would.
Cat maid to:
Jasper, male Ragdoll ?? (approx 10 yrs)
Sweet Pea, female silver tabby DSH (approx 8 yrs)
Rose semi feral, a cpietra rescue, female tabby (approx 7 yrs)
Puddles RIP (1996-2014
Snowball RIP (1991-2005)
In a cat's eye, all things belong to cats.-English Proverb
“While we are free to choose our actions, we are not free to choose the consequences of our actions.” Stephen R. Covey