Is it likely that I can prove discrimination of coverage for mental health defects?

I went out on ltd as a result of breast cancer, surgeries, complications and treatment. MetLife LTD approved my claim. At the tail end of chemo I began to experience severe depression, anxiety, struggled to get out of bed and take care of myself, suicidal thoughts etc, as well as progressing cognitive issues (either chemobrain or result of psychological issues) I tried to return to work twice but was unsuccessful and struggled significantly (I previously had outstanding/strong work history) and MetLife approved continued LTD. It’s never been my concern about what my diagnosis’s are. I’ve done extensive inpatient/outpatient, medication, ECT and therapy without progress. I’ve applied for many studies and trials but have been disqualified for one reason or another. I’ve had multiple DX as they appear to be subjective and many of them have over 60-80% overlapping symptoms. Now MetLife is denying my claim saying there is a 2 year benefit max for depression. However, we’ve since concluded I’m bipolar but irregardless BPD and MDD symptoms overlap. Recently SSD approved my claim (but benefits are si small I’m only 41) why is MetLife able to set limitations for one dx and not other? Also, I still fight to stay alive each day. If I lost my leg they would cover it period. Also, my cancer kicked off this downward spiral and there’s no limition in that DX so again, I don’t understand the denial. I don’t know the root cause of my symptoms, my cognitive issues; I don’t know if it’s PTSD from cancer treatment and loosing my breasts (I couldn’t afford implants) maybe there’s some underlying issue from that. Do you think I can prove discrimination of coverage for mental defect or treating people differently? All I want is for them to continue to cover me (60%) until I can productively return to work. Please help.