Why come on this forum if you are 100% sure that this is a behavioral issue? You came here for opinions. You got them.
There is something medically wrong with the cat. Cats do NOT a urinate/defecate because they're being vindictive. Most obviously, the vet has missed something. I feel very bad for your cat.
Please, do the cat a favor and find him a home with an owner that WILL care about him enough to find out what the real problem is.
As I said it is behavioural there is nothing medically wrong with him I am the second owner he has done this with he does this when he is angry with you. So when my youngest was in the nicu for 2 months he would soil my bed every time I left the door open. If he isn't fed what and when he wants he will vomit there it never food in it as he holds out for what he has decided he wants to eat. He has been checked so yes he is evil, As its behavioral. I'm not an idiot I have del with and rescued many cats working for rescue agencies I've seen everything under the sun but I have not had to deal with thus type of behavioural problem before. but hey Thanks for treating me like one. Have a lovely! Day.
first of all...cats aren't evil...he needs to see a Vet, he is obviously having some stomach issues, perhaps the food does not agree with him, and the inappropriate elimination is likely due to crystals in his bladder that are very painful and he is trying to tell you he hurts!!!! these are caused by feeding dry food and are most common in male cats especially older ones. sometimes eating his food to fast can also cause the vomiting, but I think there is more going on there and he needs a Vet