Often in the beginning type "unknown" is appropriate until more tests and a bit more history is written.
Make another appointment with the Endo or with another Endo. In the meantime, keep your written daily records of time of day, exact food eaten with estimated carb grams, and blood sugars before and 2 hrs after eating. Start each page with the date and your fasting blood sugar. A page a day, with times of each test. Sometimes test 1 hour after eating, too.
Do a couple weeks of low carb, then a week of eating items that spike: fruit, granola/cereal, starches. Take it to the Endo; if the endo has too little time for that appointment, ask for an appointment with his/her CDE.
"A1c too low" is not a reason for denying insulin. You seem borderline, but state you've heard your pancreatic beta cells can be given a vacationwise happy breather by taking insulin. Saving what you've got is a worthy ambition.
If all this gets you nowhere, go to another Endo or a University diabetes center. One of the ways I find Endos is by going to a hospital diabetes teaching center and asking the nurses who they'd go to. And since they won't give me only one, I say, "ok, you give me one, and you give me the 2nd one." And I go on like a zombie, saying I'll never tell....
A GP may or may not go for detailed advanced work with diabetes as he takes his required hours of continued education. Sometimes he doesn't have enough diabetes patients to have more curiosity. And regulation cannot stipulate so many hours in this aspect of diabetes and so many hours in that aspect to the degree that is needed in diabetes.
Just because you've been "sent back" does not mean you have to do it.