Therapist claims keep getting denied - what am I doing wrong?

My insurance covers mental health but every single claim from my therapist gets denied. First they said she wasnt in network (she is, I verified). Then they said the diagnosis code was wrong. Then "missing documentation."

Its been 4 months and Ive been paying out of pocket the whole time. Ive filed 3 appeals. Is there something else I should be doing? This feels deliberate.