I don’t know their situation but common tactics are to deny claims hoping that the patient will either die or find other funding options. This is an entire industry:

https://www.propublica.org/article/cigna-pxdx-medical-health...

https://www.propublica.org/article/evicore-health-insurance-...

This is one example of how hard it can be to fight these fraudulent denials, even for someone with above average resources:

https://www.propublica.org/article/priority-health-michigan-...

Individuals can’t fix these problems at scale: it needs something like a government investigator with subpoena power and the ability to directly fine executives. As long as people make more money by denying care, they’re just going to keep finding ways to do so.

The government can mandate anything it wants, if insurance companies are allowed to perpetrate mass fraudulent denials then it simply doesn't matter.

Just because it mandates coverage doesn't mean it mandates any treatment be provided in every case.

Certain expensive chemo drugs will get denied unless cheaper options are tried first, if they're used off-label or experimental. Some won't be approved until surgery, at too early a stage or if tests don't indicate elevated risk factors.

The plan may cover it, but that doesn't mean the insurance company won't find a way to deny the claim.

What you do is you deny it over and over and give a confused old woman the run-around until she's so exhausted she decides it's literally easier to die than to continue fighting. Ask me how I know.