I can't walk but Standard thinks I can work

I was a prison guard for four years. When I was cutting wood a tree fell on me rupturing disks in my back. I was ordered to go to a doctor by the state. After my termination I was placed on STD by Standard, then LTD when the 2 years were up. My claim was terminated 3 days ago. I have medical evidence (so does Standard) that I’m in chronic pain in my back and knees (an old marine corp injury that has progressively gotten worse in the past few years – service connected disability 10%). I have to use a brace and cane to walk and can’t stand for long periods of time but the Standard said I could still work as a cashier or clerk in my area even though I’m in pain all the time and can’t stand for more than 2 hours or bend down. I am still trying to fight them on my own but I need help.