I'm trying to put my feet into hot water and my son massage me before 🛏️

It's caused by blood sugar running high, so to prevent it you need to get your blood sugar consistently near normal

Since it is just burning anything you can do to improve the circulation in your feet should help

Soak them in hot water/Epsom Salts - elevate them - use a foot massager etc

But I would mention it to your doctor as well - a vascular specialist can advised what specifically you may need to do to stop it from getting worse

After the "burning" stops the next step is pretty bad pain, so you want to stop this

16 to 20 is incredibly high if you're talking about mmol/L. Are you on any insulin at the moment? Other medications?

It's like 16/20

I also had this burning of my feet, and strangely, I have not had it for a long time, since my blood sugar is under control. Under control being around 7mmol/L (which is obviously not good) but it used to be 20mmol or higher very frequently.

What are your blood sugar readings like?