I am currently taking steroids by nasal spray for a sinus problem and my bg levels are higher than I would like - say in the 7 to 10 range, but not as high as yours. I was told that this would not have a huge effect on my bg levels (although I think it has had some effect) since the application was topical, i.e. it just affects the area to which the steroids are applied and doesn't get into the rest of the body; this is in distinction to e.g. oral steroids, which spread throughout the body. I don't know what is implied by taking them using a nebuliser - did your doctor say?
Afraid I can't add anything as to how to sort this out except, as others have said, get in touch with either the doctor who prescribed them or your diabetic team.