Why is it cheaper to get a 90-day supply of my SRRI than a 30-day supply?

Tl;Dr I just got this letter and I’m confused about what they want me to do if they are aware I’m still in pain and unable to walk, but they won’t cover the treatment for me to get better? Ortho, PT, myself all recommend physical therapy but insurance keeps trying to deny coverage, and referring to the initial report from the ER after the accident instead latest and more detailed info.

Part of the letter I received

I have tendon and nerve damage and a comminuted fracture in my foot after being hit by a distracted driver in April. After the accident I went to the ER and got some initial scans done which did not show anything more than a sprain, but the ER doctor said I should see an ortho when I get home (I was out of town), so I did see my PCP, then an orthopedist and got X-rays and CT scans done and all have shown a fracture (broken in two) and a crush injury which is limiting the amount of feeling in the front half of my foot. Insurance has been awful about approving my PT from the start and has been trying to refer to the initial ER report over the most up to date, ongoing information.

All providers are in network. I have great insurance, or so I thought, but it seems my insurance uses this sub-company to manage the physical therapy part of the coverage and that is the one that’s causing the issues. They’ve been trying to deny my coverage since my second appointment even though I am supposed to be allotted 60 PT sessions per year.