Do doctors / insurance companies intentionally bill wrong?

At my gynos office last year, I got routine, preventive STD testing. I was billed for it, and when I asked the insurance rep about it, she told me STD testing wasn’t covered. This year, the same thing happened, billed again for tests that were preventive. The code they used doesn’t explain anything, seems like a general/catch all code.

So I call the insurance company again to ask what exactly I’m being billed for since they don’t provide any info. While I’m on the phone, I find a document online stating that my insurance company covers preventive STD testing (the exact tests I got). So after an hour of talking to people on the phone, I’ve filed a claim with the provider to ensure they coded it as such. If they did, I guess I have to go back to the insurance company and hassle them about it.

Is this a frequent occurrence in the healthcare industry? I’m so frustrated and feel like it’s extremely shady. Then I have to spend my precious time getting it rectified.