How can I appeal Cigna's decision if there are no written communications explanation the reasons for claim termination?

I am one of those individuals that has been receiving CIGNA benefits for two years and now has received a verbal communication, not a written notification, that my claim has been cancelled. I have been told that a CIGNA doctor and nurse who has never seen me, after reviewing my medical records, have determined that I am able to perform a job outside the profession that I worked in for over three decades. The disease that ended my career, claimed not only my physical health but has caused cognitive limitations. As time progresses my body and mind experience more and more limitations as this fatal disease claims more of me. How can I appeal this decision, especially when there are no written communications explaining the specific reasons for claim termination, process for appealing the cancellation of claim and deadlines? So individuals, like me, who have worked all their life, supported their family and community, who purchased an LTD insurance policy to protect their loved ones, come to find out that the “policy” is structured such that as you slowly die, so too your income is zeroed out and you are left to watch your family sink deeper into financial hardship, as you sit trapped in a body and mind that can do nothing to stop the nightmare. How can a family that is already financially challenged, fight an unjust ruling by a corporate behemoth?