I was having a hard time at work due to my illness. I had asked to change to a less stress
You need to talk to a lawyer right away. Many LTD policies only insure you until age 65 or retirement, whichever comes first, but if you had already agreed to stay on, then you didn’t retire. But you need to get the messaging right. https://www.resolutelegal.ca/
The language in my LTD policy says that it ends on retirement. You really need to talk to a lawyer as soon as possible about whether the notice that you gave them was effective or not. It sounds to me that you have a good argument that it wasn’t effective but you need to talk to a lawyer or you might get nothing from your LTD.