If you are officially divorced, make a copy of the divorce decree and send it along with your letters advising them that you want his name removed asap. I had the same issue, with the electric and telephone company, but when I explained that he was out to lunch, threatening to cut both off and I was living in the home, they soon got their act together and changed the bills over to my name.
I wish you all of the best in getting the house read to sell. It's a lot of work, but when that for sale sign goes up, you'll feel much better.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.