BCBS Federal cut my therapist's in-network reimbursement mid plan year and now im paying $90 more per session - is this even allowed and what are my options?

posting because im honestly not sure if what im seeing is a billing error or a legitimate plan change that nobody warned me about. ive been seeing the same LCSW for anxiety and ADHD adjustment for about 14 months. she is in network with BCBS Federal Employee Program (FEP). when i started, my cost share was $25 per session, she was reimbursed at $130 per 60 minute session, i paid the copay, BCBS paid the rest, everyone was fine.

three weeks ago her front desk calls and tells me there is an "adjustment" to her contracted rate and the new patient responsibility is $115 per session, not $25. apparently BCBS sent out a fee schedule update in early april that reduced LCSW reimbursement for the 90837 code by about 30% across the board. my therapist is honoring her in network contract but said almost half her FEP clients have called to ask whats going on.

i called BCBS and got a member services rep who kept reading off a script that said "your benefits have not changed, your in network cost share is still $25." but my therapist's office is showing me an EOB from last week where the allowed amount dropped and the "patient responsibility" line jumped. somebody is wrong here. either the EOB is misapplied or member services has no idea their network team changed reimbursement.

my questions: (1) can a carrier change in network reimbursement mid plan year without member notification? i thought benefits had to stay consistent through the plan year. (2) is there a specific phone tree at FEP to get to someone who actually has eyes on the provider contract side, not just member services? (3) has anyone successfully filed a grievance over a billing discrepancy like this and gotten the carrier to fix it on the back end? im 6 weeks from running into my deductible reset so id rather get this sorted than just eat the cost.