I have so much sympathy for you Jess
I have been there. Most of Feb I was in that dreadful pink zone. Exhausting and demoralizing


My guess is you are dealing with glucose toxicity and insulin resistance.
If you want to learn more on the medical side (what is actually going in in Charlie's body) see links on this Sticky:
https://www.felinediabetes.com/FDMB...-what-is-it-what-should-i-do-about-it.144381/
When a diabetic animal is hyperglycemic for long enough, the animal's damaged tissues may start having trouble using insulin. This in turn means that even a well-dosed animal may continue to have high blood sugar, leading to even more insulin resistance.
Various methods through this "glass floor" have been tried, to varying degrees of success. One way is to continue gradually raising insulin dosage until the tissues pick up the insulin and start absorbing glucose, then quickly back off to a lower dose. Another is to "jumpstart" the process with a fast-acting insulin or a deliberately high dose of the regular insulin, then quickly back off to a lower dose. Another is to reduce the carbohydrate content of the food further, or to eliminate dry food entirely (even low-carb dry food), thereby presenting less of an obstacle for insulin effectiveness and reducing insulin needs. Aggressive attempts to break glucose toxicity are best regarded as dangerous and should be addressed in close partnership with a diabetes-experienced veterinarian.
From here:
https://petdiabetes.fandom.com/wiki/Glucose_toxicity (one of the linked articles in the Sticky).
Basically you are in a bit of a vicious circle where his continued high numbers are making him more resistant to insulin, and because he is more resistant to insulin he has higher numbers. As I understand it here on FDMB the preferred safer approach to get out of this awful loop (rather than the more radical and risky interventions) is adopting low carb foods, which you have done already, and then the continual gradual raising of the dose, which you are busy doing - and just have to *keep doing* until the cycle breaks.
I know it can feel like you are going mad when you not only see no progress but the numbers are actually getting worse. But it is not that you are doing something wrong, it's the medical reality of the condition. You've at the stage when you are pushing and pushing at the "glass floor" and its just not ready to break yet.
Which means you just have to be patient and proceed with the increases - until you eventually get to the right dose. It happened for Noogi.
Sorry for the long post. My way of coping with FD-related stress is researching and explaining things - as much to myself as to others. I hope I have understood this correctly. If not I hope moderators or more experienced members correct me and/or add more nuance.
Lastly, I know there are some medical conditions like acromegaly that can cause extreme insulin resistance. Lots of info on this site about that, so maybe read about it just in case it might be a factor for Charlie. My guy had a blood test for it as he was extremely insulin resistant in the beginning too and the vet wanted to eliminate it.