M.,
First, I want to say that I am so sorry that this has happened. It must be devastatig for you. I will keep you and your son in my prayers.
Now for our experience with this surgery. My son developed his first ear infection when he was 6 months old. After it never fully going away during the next year and a half, he had his first set of tubes at 2 years old and his second at 3 years old. Even those did not help one iota with the infectins. He still got ear infections regularly and blew the tubes out rather quickly. We changed doctors and on our first visit the new doctor found that my son only had 10% remaining of his left drum and also had a hole in his right drum. We also discovered that he did not hear with the eardrum (because it wasn't there), but with the bones in the ear. His hearing was diminished (and always will be), but better than they had expected. We had a graft done on the drum (not the paper). The graft took, but he blew a hole in the drum again. We are currently waiting for him to get through his coming pre-teen growth spurt and we will do the surgery again. In the meantime, he can get NO water in his ears or it can cause him to go permanently deaf in that ear.
Now, I am wondering how long they waited after the surgery to do the hearing test. My son had a different kind of Tympanoplasty where the doctor cut the back of his ear and laid it over out of the way. My son had so much packing he could not have heard a thing with that ear if his life depended on it. Another thing to consider is that the ear is in a bit of shock from the surgery.
I do not know who the doctor was that you used, but I love Dr. Mark Brown with Central Park ENT in Arlington. He is fabulous. He listens to me and realizes that although his specialty is the ears, nose and throat, my specialty is my children and I know them and their "quirks" better than anyone else. He also repects my opinions as a mother. When I went to him with my daughter, I really went to see if I was right or not. She has extremely large tonsils and he agreed that they will have to be removed. He agreed that at her age (barely over 2 years), it is not wise to do them yet because she is not old enough to understand the need to be calm and sedate. He said it would go from being a few hours in the hospital to a week or two at her age. He is a parent and just a very nice man. If you have any questions, even if they do not pertain to that particular visit, he will answer them.
Again, I will keep you and your son in my prayers and thoughts. I do hope that this is a temporary thing and his hearing is restored completely.