First off Welcome to FDMB
Second most cats hate the prescription stuff...and really it isn't needed, there is nothing special about it that can't be found in regular commercial canned cat food. The real trick is that you want him on a low carb/high protein canned or raw diet. Many of us feed Fancy Feast Classics, Friskies Pate Style, or 9-lives pate, so you might try getting some of those and see if he will eat those.
Now for the questions...What insulin did the vet put him on?
What was his diet before he was dxed? And what are you trying to get him to eat now?
And can we teach you to test his BGs at home? As this is absolutely the best way to keep him safe while he is on insulin.
Lastly...Breathe...you have now found the best place you never wanted to be to help you help your furry friend.
Oh yeah...what's his name and what's your's? We are a friendly bunch here and we like to be able to call you by your name.
Mel, Maxwell, Autumn & The Fur Gang