The medical experts consider verrucas as a minor problem best left to dissapear by themselves.
The chemicals used for treatment are regarded as not suitable for diabetics, but I don't know why.
You have certainly seen all the experts and if they are stumped it's unlikely that us amateurs will have any answers.
I know they are a pain in the foot! I had some for years, they were finally removed surgically and it hurt a lot when the local wore off. They have never come back.
There are some suggestions that duct ( Duck) tape can work, do a Google.
Based on my experience, two years of various scrappings, potions, and even freezing failed to get rid of them, so maybe you can discuss surgery with your doc?
H