When you are presented with the attorney invoice showing the time spent, on what tasks the time was spent, and the money owed for that time, go over this carefully to see if there are any errors that you can legitimately dispute.
The attorney deserves to be paid for the time spent on the work he did for you and, if there is a clause in your contract saying he has earned it all, you owe it all. If there is a refund due you according to the terms of your contract, you will have the money refunded. If more money is owed than you already paid, expect to pay more.
You might want to keep in mind that the time the attorney spent on your case was time he could not spend on other pursuits, like working on a case for another client willing to pay for his services.
With that said, you are free to argue with the ailing attorney all you want. I am not sure there is much more that needs to be discussed on this forum, however.