Pre certification?

Last February I had to have an appendectomy, I went to my small town local hospital and they did an MRI confirming I had appendicitis. Since they don’t have a surgeon on call they sent me to the next town over. I basically went right into surgery when we got there. Anyways, I’m still getting mail from my insurance telling me they are not going to cover my surgery until they get pre certification documents, a letter or medical necessity and all other supporting documentation. I have called the hospital 4 times, my insurance has called twice and still nothing. I’ve called the original doctors office that diagnosed me and the surgeons office as well, my insurance company won’t talk to or give them any information since they have already settled the claim. They (insurance) is saying they can only receive info from the hospital who preformed the surgery. But they have not responded to any requests for information. Insurance is saying they will not cover anything if they don’t receive all required paperwork within 365 days. I’m freaking out, this bill is for over $20,000.