LTD claim terminated after 2 years - going into fight mode

I have fibromyalgia and spinal stenosis. After my condition got bad enough to stop working in early 2024, I went through the whole process - doctor documentation, functional assessments, everything. My employer's long-term disability insurer approved my claim and I've been receiving benefits for just over two years.

Last week I got a letter saying my claim is being terminated. Their reason was that their "independent medical review" concluded I am capable of sedentary work. I want to be clear: nobody from this company has ever examined me. This review was done by a doctor who looked at my medical records remotely and apparently decided I'm fine to work despite the fact that my actual treating doctors say otherwise.

I'm not just going to accept this. I can't. These benefits are keeping me afloat. But I'm also scared and exhausted and don't fully understand what my options are. Has anyone been through this and actually won? What should my first steps be?