I feel your pain, I really do. I too have asthma, secondary to Lupus, and I have struggled with it for years. The first thing I noticed about your post is that you say you are managing your condition at home. If you are having frequent attacks so bad that you are unable to speak or breathe, your asthma is NOT managed or under control and your doc really needs to work with you on treating the underlying cause (in my case it is chronic autoimmune inflammation unrelated to allergies).
I know that prednisone is a drug that most of us love to hate because it works to fight inflammation but it has those nasty side effects. Because I have been on massive doses in the past, both orally and via IV infusion, I can no longer take it due to its serious side effects, including avascular necrosis.
So to manage my asthma, my doctor has prescribed daily doses of Singulair tabs and an Advair inhaler, along with a rescue inhaler as needed. I also have a home nebulizer and don't go ANYWHERE without it, especially during a Lupus flare when my lung problems seem to get worse. I have far fewer attacks though since I started the Singulair/Advair regimen. Of course we are all individuals and we each respond differently to meds. But you might check with your doctor about trying something different. Maybe the Symbicort just isn't working anymore?
I'm sure you probably already know this since you have had this for so long, but I have to ask...are you checking your peak flow daily? That is very important as well. I don't know if you have done this or have one that is already marked, but I marked mine with green, yellow and red areas where the numbers are. That way you are alerted when you fall into the yellow zone and can stop a serious attack from occurring. Anyway, please keep us posted on how you are doing!