Wow, I am really having serious doubts about your vet now.
Not too difficult to determine if the kidneys are working, urinalysis combined with blood work, if necessary an ultrasound.
I really hope the feeding will get Tus back on the road to recovery.
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