High blood sugars can cause the tissue, especially on the feet, to breakdown. But so can anything that rubs or causes pressure. The first thing I would ask is how well are your blood sugars regulated. Then I would probably ask if your shoes (or prosthetic if you have one) is feel uncomfortable or is causing pressure.
If you can get your hands on some raw honey (best), you might want to try applying it to the ulcers. They have been having success with this in the US for the treatment of nonhealing diabetic ulcers that do respond with conventional treatment. Regular honey will also work, but not as quickly as the stuff straight from the hive. There are also some vitamins and supplements you could take that help improve peripheral circulation. Don't have my reference book close by, but if your interested which ones, just post and I'll get them to you. Hope this helps.
Caesarella