My cat protests when being told no

Ive had my ragdoll Hunter since he was a kitten, absolutely amazing lil dude loving, sweet, gorgeous and playful. Hes now 1y8m and his behaviour is baffling me, he can go in the kitchen whenever im not making food. When i make food i tell him to get out an he goes to his litter tray in protest and tries to squeeze whatever pee he has left in him which is causing him to strain and pee blood. In short terms he’s protesting being told no and ive already spend over £700 on unblocking him a week ago at the vets just after getting him castrated. He only started doing this once he was castrated so i dont know what to do, i cant afford another £700 unblock again just because hes not happy hes not allowed to steal food.