I believe All insurance companies deny claims as a matter of doing business. More than once, I have had to go up multiple levels of customer service to get the bill paid by the insurance company. (as it should have been) It does not fit into the insurance company's business model/profit margin to pay for their customers claims. There are only two things that can fix this, price regulation of the medical industry, or a bill of rights for insurance customers that says: if you buy insurance, all costs will be covered.

I work in the health insurance industry and look at claims all day. Insurance companies (at least mine) pay the vast majority of claims. There are occasional instances where claims are not paid because a service is not covered, and normally the reasons are clearly outlined in documentation such as the member's benefit book. To say that insurance companies don't pay most of the claims is not true. It's good to understand your insurance policy to know what to expect. Know your insurance so you can get the most benefit from it.

how can you understand all the mumbo jumbo in a "booklet". they need to make it simple and to the point. that is all

I find that when claims are not paid, it's because the service was not covered. Many people don't take the time to read the information they receive concerning their coverage. The only issue that I have had in the past when my insurer did not pay the claim was because my physicians office entered the wrong codes(which happens often).  Once they corrected it, my claims were paid. It is never smart to just settle for the first bill you receive. Pay attention to detail. This not only goes for health insurance, but for your electric service, water, etc. It makes sense to "know before you go". Know what is covered, if you are not sure, most companies customer service dept will let you know what's covered and what is not.

I usually check my benefits first to make sure the charge should have been covered; sometimes I'm wrong and it isn't. But if it should have been covered, I call the insurance company first and the doctor second if it turns out to be an issue where the doctor should have billed differently. It's amazing the difference it can make for the doctor to tweak the billing code they use. And I'm not talking fraud, it's usually a case of the billing code being too specific or not specific enough.