What is my recourse if my third party administrator short-term disability carrier is denying my claim?

I was on leave for 8 weeks and my plan allows for 26. I returned to work at half time 10 days ago because I am broke and desperate- I will need to return full time before I am physically able because I'm out of groceries, gas for the car, and need to try to access 401k funds which I can't until I am fully active again. I fell and re-injured an SI disc herniation and S1 nerve malfunctioning. Doctor advised S1, L5 and SI joint dysfunction. Got initially approved off by docs for first week and a half. Tried injections and meds so harassed docs office advising I was unable to sit without burning pain and numbness. Doc did not see me for 8 weeks. In the meantime, I fell again 4 weeks after first fall from leg weakness and lost consciousness. ER doc said I fainted and documented whiplash, which aggravated C5 C6 previous injury. So now I can't sit and have headaches. At week 7 saw a DO for an orthopedic manipulation and said how bad the pain was but asked for note to release me back to work because I was so desperate for a paycheck. Unable to go back at that point due to pain and increased aggravation from second set of injections the following week. Talked to doc who did injections and tried to explain terrific pain, STD carrier threatening to deny claim and asked what I could do- he said try to go back part time- big help. Finally saw a new MD who prescribed new meds and wanted neurosurgical consult right away- someone finally listened to the fact I'm having numbness and pain (she thought possible cauda equina). Asked her to release me to part time, which she did reluctantly due to my dire financial situation. 8.5 weeks into leave I returned. STD carrier had previously advised the "injury did not support" the need for leave since my job is sedentary- I sit at a desk in call center. That is exactly the problem, sitting exacerbates the pain and numbness. Case is up for "medical review" and I know it will be denied. How can I appeal it?