Once my car was badly damaged by someone who ran a stop sign. It was clearly the other driver's fault. Her insurance was Allstate. They strung me along for more than a month "investigating" this obvious situation.
My car was an older one that was worth about the cost of the repairs, and they probably thought I would just give it up. But it was my only transportation and I needed it for work.
I did some research on California's insurance regulations and discovered their requirement that claims be settled within 40 days. After 40 days passed, I wrote a email similar to the letter examples in this article, giving then five days before I reported them to California's insurance department.
It was astonishing to see the immediate change in their behavior. The adjustor who had been playing telephone tag for weeks called me within an hour and arranged for a body shop near my home to start work immediately.
They laugh at angry bluster, but will move mountains to appease a focused person who can bring a regulatory agency down on them.