It does sound like Coco Puff has lost his hearing due to being sick. Hopefullly your vet will have some answers and maybe it is just temporary.
My Samantha was deaf for her last year of her life and she meowed very loudly to announce that it was time to feed her or that she had just used the litter box or that she wanted someone in the room with her. Her deafness was due to her old age, Coco Puff sounds awfully young to have that be the reason that he is losing his hearing. It seems like a cat that can't hear itself meow will meow louder and louder.

My Milly is a loudmouth Meezer especially when she wants something like dinner or treats or really, really wants to go outside badly.(she is only allowed out on her leash & harness now, she used to be outside all the time at her former home)
Milly & I hope your sweet Coco Puff feels better soon and hopefully it is something temporary from being sick recently.