insurance moved my biologic off formulary mid-year and now im paying $1,400/mo cash - is there any way to fight this

looking for anyone whos been through this because im at my wits end. i have crohns and ive been stable on stelara for almost 3 years. infusion every 8 weeks, life is good, no flares. open enrollment is in november for my plan (small employer, BCBS HMO) so i didnt expect anything to change mid year.

last month i go to the specialty pharmacy for my refill and they tell me my plan moved stelara from tier 4 specialty to "non-formulary" effective june 1 and im now responsible for the full cost. the negotiated rate is something like $1,400 a month for me, which i absolutely cannot sustain. their suggestion was to switch to skyrizi which is on their preferred list now.

here is the part im confused about - can they actually do this mid-plan-year? i thought formulary changes had to wait until renewal unless theres a safety concern or generic launch. ive been on stelara stably and theres no biosimilar approved yet that i know of. my GI doc is willing to write a medical exception letter and a step therapy override but the prior auth came back denied within 24 hours which feels suspicious like nobody even read it.

has anyone successfully appealed a non-formulary exception for a biologic? do i need to escalate to an external review or hire one of those patient advocacy services? also has anyone actually switched from stelara to skyrizi after being stable for years - im terrified of triggering a flare for a coverage reason rather than a medical one.