www.diabetes.org.uk/guide-to-diabetes/managing-your-diabetes/hba1c
HbA1C is a reading which shows the accumulated damage sugars do to the blood cells. Glycated haemoglobin.
It's this glycated haemoglobin which causes nerve damage, peripheral neuropathy, reduced immunity and so forth.
Due to it's impaired ability to carry oxygen, it can make patients susceptible to infection and slows the ability to heal injuries.
Insulin converts carbohydrates and complex sugars into glucose which the body needs for fuel.
With most types of Type 2, the pancreas is still producing insulin, but the body's cells have effectively become 'immune' which is why you're taking metformin which reduces that 'immunity'.
Boring as it sounds, you need a low carb diet.
Not just a low sugar diet; a low carb diet.
Pasta, rice, potatoes, baked goods, cakes, bread etc. Must be reduced to an absolute minimum.
Yes, compared to what you're used to, this will probably feel extreme, but many Type 2 diabetics have found that they've been able to reduce their medication.