Medicare Pre-Authorization Question

I am having a rather expensive procedure in two weeks. I called Medicare to see if they pre-authorized it. They could not give me any information about it. All the Medicare representative said was that I would have to call the clinic.

Well, I already have problems with the billing department. They mailed me a bill for services a full year later. I called to find out why. They said that there was a problem with the first time they sent it to insurance and that they resubmitted it several more times and that it kept being denied. I called the insurance company and they said the first time was rejected because there were NO billing codes on it. They claim they never received another claim submission. I called the billing department and they refused to put me in touch with the billing reps that could give me the dates of submission so I could compare with insurance. They never called me back. Obviously I have not trust for them.

I called the pre-authorization representative at the clinic and she refused to say if it was authorized. She said she has "heard" that Medicare pays for the service I am receving.

Can the clinic get pre-authorization from Medicare for procedures?? 

Hopefully someone knows and can give me somewhere on the internent so I have proof. I could really use some help with this.

Thank you.